feat: add python and java solutions to lcof question

添加《剑指 Offer》题解：面试题38. 字符串的排列

Author: yanglbme

lcof/面试题38. 字符串的排列/README.md

@@ -25,14 +25,63 @@
 <!-- 这里可写当前语言的特殊实现逻辑 -->
 
 ```python
-
+class Solution:
+    def permutation(self, s: str) -> List[str]:
+        def dfs(x):
+            if x == len(s) - 1:
+                res.append("".join(chars))
+                return
+            t = set()
+            for i in range(x, len(s)):
+                if chars[i] in t:
+                    continue
+                t.add(chars[i])
+                chars[i], chars[x] = chars[x], chars[i]
+                dfs(x + 1)
+                chars[i], chars[x] = chars[x], chars[i]
+        chars, res = list(s), []
+        dfs(0)
+        return res
 ```
 
 ### Java
 <!-- 这里可写当前语言的特殊实现逻辑 -->
 
 ```java
-
+class Solution {
+    private char[] chars;
+    private List<String> res;
+
+    public String[] permutation(String s) {
+        chars = s.toCharArray();
+        res = new ArrayList<>();
+        dfs(0);
+        return res.toArray(new String[res.size()]);
+    }
+
+    private void dfs(int x) {
+        if (x == chars.length - 1) {
+            res.add(String.valueOf(chars));
+            return;
+        }
+        Set<Character> set = new HashSet<>();
+        for (int i = x; i < chars.length; ++i) {
+            if (set.contains(chars[i])) {
+                continue;
+            }
+            set.add(chars[i]);
+            swap(i, x);
+            dfs(x + 1);
+            swap(i, x);
+        }
+    }
+
+    private void swap(int i, int j) {
+        char t = chars[i];
+        chars[i] = chars[j];
+        chars[j] = t;
+    }
+}
 ```
 
 ### ...

lcof/面试题38. 字符串的排列/Solution.java

@@ -0,0 +1,34 @@
+class Solution {
+    private char[] chars;
+    private List<String> res;
+
+    public String[] permutation(String s) {
+        chars = s.toCharArray();
+        res = new ArrayList<>();
+        dfs(0);
+        return res.toArray(new String[res.size()]);
+    }
+
+    private void dfs(int x) {
+        if (x == chars.length - 1) {
+            res.add(String.valueOf(chars));
+            return;
+        }
+        Set<Character> set = new HashSet<>();
+        for (int i = x; i < chars.length; ++i) {
+            if (set.contains(chars[i])) {
+                continue;
+            }
+            set.add(chars[i]);
+            swap(i, x);
+            dfs(x + 1);
+            swap(i, x);
+        }
+    }
+
+    private void swap(int i, int j) {
+        char t = chars[i];
+        chars[i] = chars[j];
+        chars[j] = t;
+    }
+}

lcof/面试题38. 字符串的排列/Solution.py

@@ -0,0 +1,17 @@
+class Solution:
+    def permutation(self, s: str) -> List[str]:
+        def dfs(x):
+            if x == len(s) - 1:
+                res.append("".join(chars))
+                return
+            t = set()
+            for i in range(x, len(s)):
+                if chars[i] in t:
+                    continue
+                t.add(chars[i])
+                chars[i], chars[x] = chars[x], chars[i]
+                dfs(x + 1)
+                chars[i], chars[x] = chars[x], chars[i]
+        chars, res = list(s), []
+        dfs(0)
+        return res