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Update Leetcode 题解 - 搜索.md
代码经力扣判题验证；1091 改用 int[] 表示坐标，不依赖 Pair；547 的链接与题名、279 的注释、200 改为无向图；重新绘制配图，难度标注按力扣更新，示例代码块的语言标注改为 text。
This commit is contained in:
CyC2018
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-67
@@ -34,7 +34,7 @@
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## BFS
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<div align="center"> <img src="https://cs-notes-1256109796.cos.ap-guangzhou.myqcloud.com/95903878-725b-4ed9-bded-bc4aae0792a9.jpg"/> </div><br>
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<div align="center"> <img src="pics/search-bfs-layers.png" width="560px"/> </div><br>
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广度优先搜索一层一层地进行遍历，每层遍历都是以上一层遍历的结果作为起点，遍历一个距离能访问到的所有节点。需要注意的是，遍历过的节点不能再次被遍历。
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@@ -63,11 +63,11 @@
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### 1. 计算在网格中从原点到特定点的最短路径长度
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1091\. Shortest Path in Binary Matrix(Medium)
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1091\. Shortest Path in Binary Matrix (Medium)
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[Leetcode](https://leetcode.com/problems/shortest-path-in-binary-matrix/) / [力扣](https://leetcode-cn.com/problems/shortest-path-in-binary-matrix/)
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```html
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```text
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[[1,1,0,1],
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[1,0,1,0],
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[1,1,1,1],
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@@ -78,38 +78,38 @@
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```java
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public int shortestPathBinaryMatrix(int[][] grids) {
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if (grids == null || grids.length == 0 || grids[0].length == 0) {
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return -1;
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}
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int[][] direction = {{1, -1}, {1, 0}, {1, 1}, {0, -1}, {0, 1}, {-1, -1}, {-1, 0}, {-1, 1}};
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int m = grids.length, n = grids[0].length;
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Queue<Pair<Integer, Integer>> queue = new LinkedList<>();
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queue.add(new Pair<>(0, 0));
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int pathLength = 0;
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while (!queue.isEmpty()) {
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int size = queue.size();
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pathLength++;
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while (size-- > 0) {
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Pair<Integer, Integer> cur = queue.poll();
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int cr = cur.getKey(), cc = cur.getValue();
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if (grids[cr][cc] == 1) {
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continue;
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}
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if (cr == m - 1 && cc == n - 1) {
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return pathLength;
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}
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grids[cr][cc] = 1; // 标记
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for (int[] d : direction) {
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int nr = cr + d[0], nc = cc + d[1];
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if (nr < 0 || nr >= m || nc < 0 || nc >= n) {
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continue;
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}
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queue.add(new Pair<>(nr, nc));
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}
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}
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}
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if (grids == null || grids.length == 0 || grids[0].length == 0) {
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return -1;
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}
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int[][] direction = {{1, -1}, {1, 0}, {1, 1}, {0, -1}, {0, 1}, {-1, -1}, {-1, 0}, {-1, 1}};
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int m = grids.length, n = grids[0].length;
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Queue<int[]> queue = new LinkedList<>();
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queue.add(new int[]{0, 0});
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int pathLength = 0;
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while (!queue.isEmpty()) {
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int size = queue.size();
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pathLength++;
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while (size-- > 0) {
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int[] cur = queue.poll();
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int cr = cur[0], cc = cur[1];
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if (grids[cr][cc] == 1) {
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continue;
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}
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if (cr == m - 1 && cc == n - 1) {
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return pathLength;
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}
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grids[cr][cc] = 1; // 标记
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for (int[] d : direction) {
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int nr = cr + d[0], nc = cc + d[1];
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if (nr < 0 || nr >= m || nc < 0 || nc >= n) {
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continue;
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}
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queue.add(new int[]{nr, nc});
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}
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}
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}
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return -1;
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}
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```
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### 2. 组成整数的最小平方数数量
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@@ -118,7 +118,7 @@ public int shortestPathBinaryMatrix(int[][] grids) {
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[Leetcode](https://leetcode.com/problems/perfect-squares/description/) / [力扣](https://leetcode-cn.com/problems/perfect-squares/description/)
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```html
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```text
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For example, given n = 12, return 3 because 12 = 4 + 4 + 4; given n = 13, return 2 because 13 = 4 + 9.
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```
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@@ -161,7 +161,7 @@ public int numSquares(int n) {
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}
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/**
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* 生成小于 n 的平方数序列
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* 生成小于等于 n 的平方数序列
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* @return 1,4,9,...
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*/
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private List<Integer> generateSquares(int n) {
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@@ -179,11 +179,11 @@ private List<Integer> generateSquares(int n) {
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### 3. 最短单词路径
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127\. Word Ladder (Medium)
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127\. Word Ladder (Hard)
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[Leetcode](https://leetcode.com/problems/word-ladder/description/) / [力扣](https://leetcode-cn.com/problems/word-ladder/description/)
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```html
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```text
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Input:
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beginWord = "hit",
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endWord = "cog",
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@@ -195,7 +195,7 @@ Explanation: As one shortest transformation is "hit" -> "hot" -> "dot" -> "dog"
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return its length 5.
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```
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```html
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```text
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Input:
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beginWord = "hit"
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endWord = "cog"
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@@ -277,11 +277,11 @@ private int getShortestPath(List<Integer>[] graphic, int start, int end) {
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## DFS
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<div align="center"> <img src="https://cs-notes-1256109796.cos.ap-guangzhou.myqcloud.com/74dc31eb-6baa-47ea-ab1c-d27a0ca35093.png"/> </div><br>
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<div align="center"> <img src="pics/search-dfs-order.png" width="640px"/> </div><br>
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广度优先搜索一层一层遍历，每一层得到的所有新节点，要用队列存储起来以备下一层遍历的时候再遍历。
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而深度优先搜索在得到一个新节点时立即对新节点进行遍历：从节点 0 出发开始遍历，得到到新节点 6 时，立马对新节点 6 进行遍历，得到新节点 4；如此反复以这种方式遍历新节点，直到没有新节点了，此时返回。返回到根节点 0 的情况是，继续对根节点 0 进行遍历，得到新节点 2，然后继续以上步骤。
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而深度优先搜索在得到一个新节点时立即对新节点进行遍历：从节点 0 出发开始遍历，得到新节点 6 时，立马对新节点 6 进行遍历，得到新节点 4；如此反复以这种方式遍历新节点，直到没有新节点了，此时返回。返回到根节点 0 的情况是，继续对根节点 0 进行遍历，得到新节点 2，然后继续以上步骤。
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从一个节点出发，使用 DFS 对一个图进行遍历时，能够遍历到的节点都是从初始节点可达的，DFS 常用来求解这种 **可达性** 问题。
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@@ -296,7 +296,7 @@ private int getShortestPath(List<Integer>[] graphic, int start, int end) {
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[Leetcode](https://leetcode.com/problems/max-area-of-island/description/) / [力扣](https://leetcode-cn.com/problems/max-area-of-island/description/)
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```html
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```text
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[[0,0,1,0,0,0,0,1,0,0,0,0,0],
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[0,0,0,0,0,0,0,1,1,1,0,0,0],
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[0,1,1,0,1,0,0,0,0,0,0,0,0],
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@@ -345,7 +345,7 @@ private int dfs(int[][] grid, int r, int c) {
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[Leetcode](https://leetcode.com/problems/number-of-islands/description/) / [力扣](https://leetcode-cn.com/problems/number-of-islands/description/)
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```html
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```text
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Input:
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11000
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11000
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@@ -355,7 +355,7 @@ Input:
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Output: 3
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```
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可以将矩阵表示看成一张有向图。
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可以将矩阵表示看成一张无向图。
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```java
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private int m, n;
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@@ -392,11 +392,11 @@ private void dfs(char[][] grid, int i, int j) {
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### 3. 好友关系的连通分量数目
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547\. Friend Circles (Medium)
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547\. Number of Provinces (Medium)
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[Leetcode](https://leetcode.com/problems/friend-circles/description/) / [力扣](https://leetcode-cn.com/problems/friend-circles/description/)
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[Leetcode](https://leetcode.com/problems/number-of-provinces/description/) / [力扣](https://leetcode-cn.com/problems/number-of-provinces/description/)
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```html
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```text
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Input:
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[[1,1,0],
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[1,1,0],
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@@ -442,7 +442,7 @@ private void dfs(int[][] M, int i, boolean[] hasVisited) {
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[Leetcode](https://leetcode.com/problems/surrounded-regions/description/) / [力扣](https://leetcode-cn.com/problems/surrounded-regions/description/)
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```html
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```text
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For example,
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X X X X
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X O O X
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@@ -509,7 +509,7 @@ private void dfs(char[][] board, int r, int c) {
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[Leetcode](https://leetcode.com/problems/pacific-atlantic-water-flow/description/) / [力扣](https://leetcode-cn.com/problems/pacific-atlantic-water-flow/description/)
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```html
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```text
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Given the following 5x5 matrix:
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Pacific ~ ~ ~ ~ ~
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@@ -599,9 +599,9 @@ Backtracking（回溯）属于 DFS。
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[Leetcode](https://leetcode.com/problems/letter-combinations-of-a-phone-number/description/) / [力扣](https://leetcode-cn.com/problems/letter-combinations-of-a-phone-number/description/)
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<div align="center"> <img src="https://cs-notes-1256109796.cos.ap-guangzhou.myqcloud.com/9823768c-212b-4b1a-b69a-b3f59e07b977.jpg"/> </div><br>
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<div align="center"> <img src="pics/search-phone-keypad.png" width="700px"/> </div><br>
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```html
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```text
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Input:Digit string "23"
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Output: ["ad", "ae", "af", "bd", "be", "bf", "cd", "ce", "cf"].
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```
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@@ -635,11 +635,11 @@ private void doCombination(StringBuilder prefix, List<String> combinations, fina
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### 2. IP 地址划分
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93\. Restore IP Addresses(Medium)
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93\. Restore IP Addresses (Medium)
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[Leetcode](https://leetcode.com/problems/restore-ip-addresses/description/) / [力扣](https://leetcode-cn.com/problems/restore-ip-addresses/description/)
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```html
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```text
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Given "25525511135",
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return ["255.255.11.135", "255.255.111.35"].
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```
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@@ -682,7 +682,7 @@ private void doRestore(int k, StringBuilder tempAddress, List<String> addresses,
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[Leetcode](https://leetcode.com/problems/word-search/description/) / [力扣](https://leetcode-cn.com/problems/word-search/description/)
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```html
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```text
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For example,
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Given board =
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[
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@@ -753,7 +753,7 @@ private boolean backtracking(int curLen, int r, int c, boolean[][] visited, fina
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[Leetcode](https://leetcode.com/problems/binary-tree-paths/description/) / [力扣](https://leetcode-cn.com/problems/binary-tree-paths/description/)
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```html
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```text
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1
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/ \
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2 3
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@@ -761,7 +761,7 @@ private boolean backtracking(int curLen, int r, int c, boolean[][] visited, fina
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5
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```
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```html
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```text
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["1->2->5", "1->3"]
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```
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@@ -813,7 +813,7 @@ private String buildPath(List<Integer> values) {
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[Leetcode](https://leetcode.com/problems/permutations/description/) / [力扣](https://leetcode-cn.com/problems/permutations/description/)
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```html
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```text
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[1,2,3] have the following permutations:
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[
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[1,2,3],
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@@ -858,7 +858,7 @@ private void backtracking(List<Integer> permuteList, List<List<Integer>> permute
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[Leetcode](https://leetcode.com/problems/permutations-ii/description/) / [力扣](https://leetcode-cn.com/problems/permutations-ii/description/)
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```html
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```text
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[1,1,2] have the following unique permutations:
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[[1,1,2], [1,2,1], [2,1,1]]
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```
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@@ -905,7 +905,7 @@ private void backtracking(List<Integer> permuteList, List<List<Integer>> permute
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[Leetcode](https://leetcode.com/problems/combinations/description/) / [力扣](https://leetcode-cn.com/problems/combinations/description/)
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```html
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```text
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If n = 4 and k = 2, a solution is:
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[
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[2,4],
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@@ -944,7 +944,7 @@ private void backtracking(List<Integer> combineList, List<List<Integer>> combina
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[Leetcode](https://leetcode.com/problems/combination-sum/description/) / [力扣](https://leetcode-cn.com/problems/combination-sum/description/)
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```html
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```text
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given candidate set [2, 3, 6, 7] and target 7,
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A solution set is:
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[[7],[2, 2, 3]]
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@@ -980,7 +980,7 @@ private void backtracking(List<Integer> tempCombination, List<List<Integer>> com
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[Leetcode](https://leetcode.com/problems/combination-sum-ii/description/) / [力扣](https://leetcode-cn.com/problems/combination-sum-ii/description/)
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```html
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```text
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For example, given candidate set [10, 1, 2, 7, 6, 1, 5] and target 8,
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A solution set is:
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[
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@@ -1027,7 +1027,7 @@ private void backtracking(List<Integer> tempCombination, List<List<Integer>> com
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[Leetcode](https://leetcode.com/problems/combination-sum-iii/description/) / [力扣](https://leetcode-cn.com/problems/combination-sum-iii/description/)
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```html
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```text
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Input: k = 3, n = 9
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Output:
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@@ -1102,7 +1102,7 @@ private void backtracking(int start, List<Integer> tempSubset, List<List<Integer
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[Leetcode](https://leetcode.com/problems/subsets-ii/description/) / [力扣](https://leetcode-cn.com/problems/subsets-ii/description/)
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||||
|
||||
```html
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```text
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For example,
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If nums = [1,2,2], a solution is:
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@@ -1154,7 +1154,7 @@ private void backtracking(int start, List<Integer> tempSubset, List<List<Integer
|
||||
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||||
[Leetcode](https://leetcode.com/problems/palindrome-partitioning/description/) / [力扣](https://leetcode-cn.com/problems/palindrome-partitioning/description/)
|
||||
|
||||
```html
|
||||
```text
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||||
For example, given s = "aab",
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Return
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||||
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||||
@@ -1202,7 +1202,7 @@ private boolean isPalindrome(String s, int begin, int end) {
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||||
[Leetcode](https://leetcode.com/problems/sudoku-solver/description/) / [力扣](https://leetcode-cn.com/problems/sudoku-solver/description/)
|
||||
|
||||
<div align="center"> <img src="https://cs-notes-1256109796.cos.ap-guangzhou.myqcloud.com/0e8fdc96-83c1-4798-9abe-45fc91d70b9d.png"/> </div><br>
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<div align="center"> <img src="pics/search-sudoku.png" width="330px"/> </div><br>
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||||
|
||||
```java
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private boolean[][] rowsUsed = new boolean[9][10];
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@@ -1261,7 +1261,7 @@ private int cubeNum(int i, int j) {
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||||
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||||
[Leetcode](https://leetcode.com/problems/n-queens/description/) / [力扣](https://leetcode-cn.com/problems/n-queens/description/)
|
||||
|
||||
<div align="center"> <img src="https://cs-notes-1256109796.cos.ap-guangzhou.myqcloud.com/067b310c-6877-40fe-9dcf-10654e737485.jpg"/> </div><br>
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||||
<div align="center"> <img src="pics/search-n-queens.png" width="500px"/> </div><br>
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||||
|
||||
在 n\*n 的矩阵中摆放 n 个皇后，并且每个皇后不能在同一行，同一列，同一对角线上，求所有的 n 皇后的解。
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@@ -1269,12 +1269,12 @@ private int cubeNum(int i, int j) {
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45 度对角线标记数组的长度为 2 \* n - 1，通过下图可以明确 (r, c) 的位置所在的数组下标为 r + c。
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||||
|
||||
<div align="center"> <img src="https://cs-notes-1256109796.cos.ap-guangzhou.myqcloud.com/9c422923-1447-4a3b-a4e1-97e663738187.jpg" width="300px"> </div><br>
|
||||
<div align="center"> <img src="pics/search-n-queens-diag45.png" width="420px"/> </div><br>
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||||
|
||||
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||||
135 度对角线标记数组的长度也是 2 \* n - 1，(r, c) 的位置所在的数组下标为 n - 1 - (r - c)。
|
||||
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||||
<div align="center"> <img src="https://cs-notes-1256109796.cos.ap-guangzhou.myqcloud.com/7a85e285-e152-4116-b6dc-3fab27ba9437.jpg" width="300px"> </div><br>
|
||||
<div align="center"> <img src="pics/search-n-queens-diag135.png" width="420px"/> </div><br>
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```java
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private List<List<String>> solutions;
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Reference in New Issue
Block a user