Update 38. 字符串的排列.md

题目链接改为力扣中的对应题目，题目描述和代码按该题的接口调整。

notes/38. 字符串的排列.md

@@ -1,6 +1,6 @@
 # 38. 字符串的排列
 
-[NowCoder](https://www.nowcoder.com/practice/fe6b651b66ae47d7acce78ffdd9a96c7?tpId=13&tqId=11180&tPage=1&rp=1&ru=/ta/coding-interviews&qru=/ta/coding-interviews/question-ranking&from=cyc_github)
+[Leetcode](https://leetcode.cn/problems/zi-fu-chuan-de-pai-lie-lcof/)
 
 ## 题目描述
 
@@ -9,15 +9,16 @@
 ## 解题思路
 
 ```java
-private ArrayList<String> ret = new ArrayList<>();
+private List<String> ret = new ArrayList<>();
 
-public ArrayList<String> Permutation(String str) {
-    if (str.length() == 0)
-        return ret;
-    char[] chars = str.toCharArray();
+public String[] goodsOrder(String goods) {
+    if (goods == null || goods.length() == 0)
+        return new String[0];
+    ret.clear();
+    char[] chars = goods.toCharArray();
     Arrays.sort(chars);
     backtracking(chars, new boolean[chars.length], new StringBuilder());
-    return ret;
+    return ret.toArray(new String[ret.size()]);
 }
 
 private void backtracking(char[] chars, boolean[] hasUsed, StringBuilder s) {