diff --git a/notes/Leetcode 题解 - 搜索.md b/notes/Leetcode 题解 - 搜索.md index 81fe3ff3..20496896 100644 --- a/notes/Leetcode 题解 - 搜索.md +++ b/notes/Leetcode 题解 - 搜索.md @@ -34,7 +34,7 @@ ## BFS -

+

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。 @@ -63,11 +63,11 @@ ### 1. 计算在网格中从原点到特定点的最短路径长度 -1091\. Shortest Path in Binary Matrix(Medium) +1091\. Shortest Path in Binary Matrix (Medium) [Leetcode](https://leetcode.com/problems/shortest-path-in-binary-matrix/) / [力扣](https://leetcode-cn.com/problems/shortest-path-in-binary-matrix/) -```html +```text [[1,1,0,1], [1,0,1,0], [1,1,1,1], @@ -78,38 +78,38 @@ ```java public int shortestPathBinaryMatrix(int[][] grids) { - if (grids == null || grids.length == 0 || grids[0].length == 0) { - return -1; - } - int[][] direction = {{1, -1}, {1, 0}, {1, 1}, {0, -1}, {0, 1}, {-1, -1}, {-1, 0}, {-1, 1}}; - int m = grids.length, n = grids[0].length; - Queue> queue = new LinkedList<>(); - queue.add(new Pair<>(0, 0)); - int pathLength = 0; - while (!queue.isEmpty()) { - int size = queue.size(); - pathLength++; - while (size-- > 0) { - Pair cur = queue.poll(); - int cr = cur.getKey(), cc = cur.getValue(); - if (grids[cr][cc] == 1) { - continue; - } - if (cr == m - 1 && cc == n - 1) { - return pathLength; - } - grids[cr][cc] = 1; // 标记 - for (int[] d : direction) { - int nr = cr + d[0], nc = cc + d[1]; - if (nr < 0 || nr >= m || nc < 0 || nc >= n) { - continue; - } - queue.add(new Pair<>(nr, nc)); - } - } - } + if (grids == null || grids.length == 0 || grids[0].length == 0) { return -1; } + int[][] direction = {{1, -1}, {1, 0}, {1, 1}, {0, -1}, {0, 1}, {-1, -1}, {-1, 0}, {-1, 1}}; + int m = grids.length, n = grids[0].length; + Queue queue = new LinkedList<>(); + queue.add(new int[]{0, 0}); + int pathLength = 0; + while (!queue.isEmpty()) { + int size = queue.size(); + pathLength++; + while (size-- > 0) { + int[] cur = queue.poll(); + int cr = cur[0], cc = cur[1]; + if (grids[cr][cc] == 1) { + continue; + } + if (cr == m - 1 && cc == n - 1) { + return pathLength; + } + grids[cr][cc] = 1; // 标记 + for (int[] d : direction) { + int nr = cr + d[0], nc = cc + d[1]; + if (nr < 0 || nr >= m || nc < 0 || nc >= n) { + continue; + } + queue.add(new int[]{nr, nc}); + } + } + } + return -1; +} ``` ### 2. 组成整数的最小平方数数量 @@ -118,7 +118,7 @@ public int shortestPathBinaryMatrix(int[][] grids) { [Leetcode](https://leetcode.com/problems/perfect-squares/description/) / [力扣](https://leetcode-cn.com/problems/perfect-squares/description/) -```html +```text For example, given n = 12, return 3 because 12 = 4 + 4 + 4; given n = 13, return 2 because 13 = 4 + 9. ``` @@ -161,7 +161,7 @@ public int numSquares(int n) { } /** - * 生成小于 n 的平方数序列 + * 生成小于等于 n 的平方数序列 * @return 1,4,9,... */ private List generateSquares(int n) { @@ -179,11 +179,11 @@ private List generateSquares(int n) { ### 3. 最短单词路径 -127\. Word Ladder (Medium) +127\. Word Ladder (Hard) [Leetcode](https://leetcode.com/problems/word-ladder/description/) / [力扣](https://leetcode-cn.com/problems/word-ladder/description/) -```html +```text Input: beginWord = "hit", endWord = "cog", @@ -195,7 +195,7 @@ Explanation: As one shortest transformation is "hit" -> "hot" -> "dot" -> "dog" return its length 5. ``` -```html +```text Input: beginWord = "hit" endWord = "cog" @@ -277,11 +277,11 @@ private int getShortestPath(List[] graphic, int start, int end) { ## DFS -

+

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。 -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。 +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。 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。 @@ -296,7 +296,7 @@ private int getShortestPath(List[] graphic, int start, int end) { [Leetcode](https://leetcode.com/problems/max-area-of-island/description/) / [力扣](https://leetcode-cn.com/problems/max-area-of-island/description/) -```html +```text [[0,0,1,0,0,0,0,1,0,0,0,0,0], [0,0,0,0,0,0,0,1,1,1,0,0,0], [0,1,1,0,1,0,0,0,0,0,0,0,0], @@ -345,7 +345,7 @@ private int dfs(int[][] grid, int r, int c) { [Leetcode](https://leetcode.com/problems/number-of-islands/description/) / [力扣](https://leetcode-cn.com/problems/number-of-islands/description/) -```html +```text Input: 11000 11000 @@ -355,7 +355,7 @@ Input: Output: 3 ``` -可以将矩阵表示看成一张有向图。 +可以将矩阵表示看成一张无向图。 ```java private int m, n; @@ -392,11 +392,11 @@ private void dfs(char[][] grid, int i, int j) { ### 3. 好友关系的连通分量数目 -547\. Friend Circles (Medium) +547\. Number of Provinces (Medium) -[Leetcode](https://leetcode.com/problems/friend-circles/description/) / [力扣](https://leetcode-cn.com/problems/friend-circles/description/) +[Leetcode](https://leetcode.com/problems/number-of-provinces/description/) / [力扣](https://leetcode-cn.com/problems/number-of-provinces/description/) -```html +```text Input: [[1,1,0], [1,1,0], @@ -442,7 +442,7 @@ private void dfs(int[][] M, int i, boolean[] hasVisited) { [Leetcode](https://leetcode.com/problems/surrounded-regions/description/) / [力扣](https://leetcode-cn.com/problems/surrounded-regions/description/) -```html +```text For example, X X X X X O O X @@ -509,7 +509,7 @@ private void dfs(char[][] board, int r, int c) { [Leetcode](https://leetcode.com/problems/pacific-atlantic-water-flow/description/) / [力扣](https://leetcode-cn.com/problems/pacific-atlantic-water-flow/description/) -```html +```text Given the following 5x5 matrix: Pacific ~ ~ ~ ~ ~ @@ -599,9 +599,9 @@ Backtracking（回溯）属于 DFS。 [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/) -

+

-```html +```text Input:Digit string "23" Output: ["ad", "ae", "af", "bd", "be", "bf", "cd", "ce", "cf"]. ``` @@ -635,11 +635,11 @@ private void doCombination(StringBuilder prefix, List combinations, fina ### 2. IP 地址划分 -93\. Restore IP Addresses(Medium) +93\. Restore IP Addresses (Medium) [Leetcode](https://leetcode.com/problems/restore-ip-addresses/description/) / [力扣](https://leetcode-cn.com/problems/restore-ip-addresses/description/) -```html +```text Given "25525511135", return ["255.255.11.135", "255.255.111.35"]. ``` @@ -682,7 +682,7 @@ private void doRestore(int k, StringBuilder tempAddress, List addresses, [Leetcode](https://leetcode.com/problems/word-search/description/) / [力扣](https://leetcode-cn.com/problems/word-search/description/) -```html +```text For example, Given board = [ @@ -753,7 +753,7 @@ private boolean backtracking(int curLen, int r, int c, boolean[][] visited, fina [Leetcode](https://leetcode.com/problems/binary-tree-paths/description/) / [力扣](https://leetcode-cn.com/problems/binary-tree-paths/description/) -```html +```text 1 / \ 2 3 @@ -761,7 +761,7 @@ private boolean backtracking(int curLen, int r, int c, boolean[][] visited, fina 5 ``` -```html +```text ["1->2->5", "1->3"] ``` @@ -813,7 +813,7 @@ private String buildPath(List values) { [Leetcode](https://leetcode.com/problems/permutations/description/) / [力扣](https://leetcode-cn.com/problems/permutations/description/) -```html +```text [1,2,3] have the following permutations: [ [1,2,3], @@ -858,7 +858,7 @@ private void backtracking(List permuteList, List> permute [Leetcode](https://leetcode.com/problems/permutations-ii/description/) / [力扣](https://leetcode-cn.com/problems/permutations-ii/description/) -```html +```text [1,1,2] have the following unique permutations: [[1,1,2], [1,2,1], [2,1,1]] ``` @@ -905,7 +905,7 @@ private void backtracking(List permuteList, List> permute [Leetcode](https://leetcode.com/problems/combinations/description/) / [力扣](https://leetcode-cn.com/problems/combinations/description/) -```html +```text If n = 4 and k = 2, a solution is: [ [2,4], @@ -944,7 +944,7 @@ private void backtracking(List combineList, List> combina [Leetcode](https://leetcode.com/problems/combination-sum/description/) / [力扣](https://leetcode-cn.com/problems/combination-sum/description/) -```html +```text given candidate set [2, 3, 6, 7] and target 7, A solution set is: [[7],[2, 2, 3]] @@ -980,7 +980,7 @@ private void backtracking(List tempCombination, List> com [Leetcode](https://leetcode.com/problems/combination-sum-ii/description/) / [力扣](https://leetcode-cn.com/problems/combination-sum-ii/description/) -```html +```text For example, given candidate set [10, 1, 2, 7, 6, 1, 5] and target 8, A solution set is: [ @@ -1027,7 +1027,7 @@ private void backtracking(List tempCombination, List> com [Leetcode](https://leetcode.com/problems/combination-sum-iii/description/) / [力扣](https://leetcode-cn.com/problems/combination-sum-iii/description/) -```html +```text Input: k = 3, n = 9 Output: @@ -1102,7 +1102,7 @@ private void backtracking(int start, List tempSubset, List tempSubset, List
+

```java private boolean[][] rowsUsed = new boolean[9][10]; @@ -1261,7 +1261,7 @@ private int cubeNum(int i, int j) { [Leetcode](https://leetcode.com/problems/n-queens/description/) / [力扣](https://leetcode-cn.com/problems/n-queens/description/) -

+

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。 @@ -1269,12 +1269,12 @@ private int cubeNum(int i, int j) { 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。 -

+

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)。 -

+

```java private List> solutions; diff --git a/notes/pics/search-bfs-layers.png b/notes/pics/search-bfs-layers.png new file mode 100644 index 00000000..ea4c15f0 Binary files /dev/null and b/notes/pics/search-bfs-layers.png differ diff --git a/notes/pics/search-dfs-order.png b/notes/pics/search-dfs-order.png new file mode 100644 index 00000000..6b18b89d Binary files /dev/null and b/notes/pics/search-dfs-order.png differ diff --git a/notes/pics/search-n-queens-diag135.png b/notes/pics/search-n-queens-diag135.png new file mode 100644 index 00000000..bb4a36b7 Binary files /dev/null and b/notes/pics/search-n-queens-diag135.png differ diff --git a/notes/pics/search-n-queens-diag45.png b/notes/pics/search-n-queens-diag45.png new file mode 100644 index 00000000..fe3aaf5d Binary files /dev/null and b/notes/pics/search-n-queens-diag45.png differ diff --git a/notes/pics/search-n-queens.png b/notes/pics/search-n-queens.png new file mode 100644 index 00000000..720f336b Binary files /dev/null and b/notes/pics/search-n-queens.png differ diff --git a/notes/pics/search-phone-keypad.png b/notes/pics/search-phone-keypad.png new file mode 100644 index 00000000..7e223e68 Binary files /dev/null and b/notes/pics/search-phone-keypad.png differ diff --git a/notes/pics/search-sudoku.png b/notes/pics/search-sudoku.png new file mode 100644 index 00000000..9cef4e47 Binary files /dev/null and b/notes/pics/search-sudoku.png differ