diff --git "a/notes/10.1 \346\226\220\346\263\242\351\202\243\345\245\221\346\225\260\345\210\227.md" "b/notes/10.1 \346\226\220\346\263\242\351\202\243\345\245\221\346\225\260\345\210\227.md"
index 63fd6d7fac656b8d2e6fd10105565f04a62545d5..fd9e836bc188a4f887393660c4e9f43c2431389e 100644
--- "a/notes/10.1 \346\226\220\346\263\242\351\202\243\345\245\221\346\225\260\345\210\227.md"	
+++ "b/notes/10.1 \346\226\220\346\263\242\351\202\243\345\245\221\346\225\260\345\210\227.md"	
@@ -2,7 +2,7 @@
 
 ## 题目链接
 
-[NowCoder](https://www.nowcoder.com/practice/c6c7742f5ba7442aada113136ddea0c3?tpId=13&tqId=11160&tPage=1&rp=1&ru=/ta/coding-interviews&qru=/ta/coding-interviews/question-ranking&from=cyc_github)
+[牛客网](https://www.nowcoder.com/practice/c6c7742f5ba7442aada113136ddea0c3?tpId=13&tqId=11160&tPage=1&rp=1&ru=/ta/coding-interviews&qru=/ta/coding-interviews/question-ranking&from=cyc_github)
 
 ## 题目描述
 
diff --git "a/notes/10.2 \347\237\251\345\275\242\350\246\206\347\233\226.md" "b/notes/10.2 \347\237\251\345\275\242\350\246\206\347\233\226.md"
index 56e244a57d7ab3675974fcc2da44430badf98cf1..01e833f70908add7dc816b81b7f708801d581346 100644
--- "a/notes/10.2 \347\237\251\345\275\242\350\246\206\347\233\226.md"	
+++ "b/notes/10.2 \347\237\251\345\275\242\350\246\206\347\233\226.md"	
@@ -2,7 +2,7 @@
 
 ## 题目链接
 
-[NowCoder](https://www.nowcoder.com/practice/72a5a919508a4251859fb2cfb987a0e6?tpId=13&tqId=11163&tPage=1&rp=1&ru=/ta/coding-interviews&qru=/ta/coding-interviews/question-ranking&from=cyc_github)
+[牛客网](https://www.nowcoder.com/practice/72a5a919508a4251859fb2cfb987a0e6?tpId=13&tqId=11163&tPage=1&rp=1&ru=/ta/coding-interviews&qru=/ta/coding-interviews/question-ranking&from=cyc_github)
 
 ## 题目描述
 
@@ -27,7 +27,7 @@
 <div align="center"> <img src="https://cs-notes-1256109796.cos.ap-guangzhou.myqcloud.com/508c6e52-9f93-44ed-b6b9-e69050e14807.jpg" width="370px"> </div><br>
 
 ```java
-public int RectCover(int n) {
+public int rectCover(int n) {
     if (n <= 2)
         return n;
     int pre2 = 1, pre1 = 2;
diff --git "a/notes/10.3 \350\267\263\345\217\260\351\230\266.md" "b/notes/10.3 \350\267\263\345\217\260\351\230\266.md"
index 4cf0ee43f686f324e91f7194106aaf5a2143b2b2..2072cb90089ab56ba9ca44bae6361c9394833b56 100644
--- "a/notes/10.3 \350\267\263\345\217\260\351\230\266.md"	
+++ "b/notes/10.3 \350\267\263\345\217\260\351\230\266.md"	
@@ -2,7 +2,7 @@
 
 ## 题目链接
 
-[NowCoder](https://www.nowcoder.com/practice/8c82a5b80378478f9484d87d1c5f12a4?tpId=13&tqId=11161&tPage=1&rp=1&ru=/ta/coding-interviews&qru=/ta/coding-interviews/question-ranking&from=cyc_github)
+[牛客网](https://www.nowcoder.com/practice/8c82a5b80378478f9484d87d1c5f12a4?tpId=13&tqId=11161&tPage=1&rp=1&ru=/ta/coding-interviews&qru=/ta/coding-interviews/question-ranking&from=cyc_github)
 
 ## 题目描述
 
diff --git "a/notes/10.4 \345\217\230\346\200\201\350\267\263\345\217\260\351\230\266.md" "b/notes/10.4 \345\217\230\346\200\201\350\267\263\345\217\260\351\230\266.md"
index 605ce19637fd355c186d8d0cf87df3fa10d02dd2..f6099a1723cdfbe8768e5ec0d724e94dba1c1892 100644
--- "a/notes/10.4 \345\217\230\346\200\201\350\267\263\345\217\260\351\230\266.md"	
+++ "b/notes/10.4 \345\217\230\346\200\201\350\267\263\345\217\260\351\230\266.md"	
@@ -2,7 +2,7 @@
 
 ## 题目链接
 
-[NowCoder](https://www.nowcoder.com/practice/22243d016f6b47f2a6928b4313c85387?tpId=13&tqId=11162&tPage=1&rp=1&ru=/ta/coding-interviews&qru=/ta/coding-interviews/question-ranking&from=cyc_github)
+[牛客网](https://www.nowcoder.com/practice/22243d016f6b47f2a6928b4313c85387?tpId=13&tqId=11162&tPage=1&rp=1&ru=/ta/coding-interviews&qru=/ta/coding-interviews/question-ranking&from=cyc_github)
 
 ## 题目描述
 
@@ -15,7 +15,7 @@
 ### 动态规划
 
 ```java
-public int JumpFloorII(int target) {
+public int jumpFloorII(int target) {
     int[] dp = new int[target];
     Arrays.fill(dp, 1);
     for (int i = 1; i < target; i++)
diff --git "a/notes/12. \347\237\251\351\230\265\344\270\255\347\232\204\350\267\257\345\276\204.md" "b/notes/12. \347\237\251\351\230\265\344\270\255\347\232\204\350\267\257\345\276\204.md"
index 913d9fe39ed817b7ea8d9a4da1ea0eaec6690541..157785374b3fa646159e43cbe22e5dbb78c8ee5e 100644
--- "a/notes/12. \347\237\251\351\230\265\344\270\255\347\232\204\350\267\257\345\276\204.md"	
+++ "b/notes/12. \347\237\251\351\230\265\344\270\255\347\232\204\350\267\257\345\276\204.md"	
@@ -1,6 +1,6 @@
 # 12. 矩阵中的路径
 
-[NowCoder](https://www.nowcoder.com/practice/c61c6999eecb4b8f88a98f66b273a3cc?tpId=13&tqId=11218&tPage=1&rp=1&ru=/ta/coding-interviews&qru=/ta/coding-interviews/question-ranking&from=cyc_github)
+[牛客网](https://www.nowcoder.com/practice/69fe7a584f0a445da1b6652978de5c38?tpId=13&tqId=11218&tab=answerKey&from=cyc_github)
 
 ## 题目描述
 
@@ -19,46 +19,60 @@
 本题的输入是数组而不是矩阵（二维数组），因此需要先将数组转换成矩阵。
 
 ```java
-private final static int[][] next = {{0, -1}, {0, 1}, {-1, 0}, {1, 0}};
-private int rows;
-private int cols;
-
-public boolean hasPath(char[] array, int rows, int cols, char[] str) {
-    if (rows == 0 || cols == 0) return false;
-    this.rows = rows;
-    this.cols = cols;
-    boolean[][] marked = new boolean[rows][cols];
-    char[][] matrix = buildMatrix(array);
-    for (int i = 0; i < rows; i++)
-        for (int j = 0; j < cols; j++)
-            if (backtracking(matrix, str, marked, 0, i, j))
-                return true;
+public class Solution {
+    private final static int[][] next = {{0, -1}, {0, 1}, {-1, 0}, {1, 0}};
+    private int rows;
+    private int cols;
+
+    public boolean hasPath (String val, int rows, int cols, String path) {
+        if (rows == 0 || cols == 0) return false;
+        this.rows = rows;
+        this.cols = cols;
+        char[] array = val.toCharArray();
+        char[][] matrix = buildMatrix(array);
+        char[] pathList = path.toCharArray();
+        boolean[][] marked = new boolean[rows][cols];
+        for (int i = 0; i < rows; i++)
+            for (int j = 0; j < cols; j++)
+                if (backtracking(matrix, pathList, marked, 0, i, j))
+                    return true;
 
-    return false;
-}
+        return false;
+    }
 
-private boolean backtracking(char[][] matrix, char[] str,
-                             boolean[][] marked, int pathLen, int r, int c) {
+    private boolean backtracking(char[][] matrix, char[] pathList,
+                                 boolean[][] marked, int pathLen, int r, int c) {
 
-    if (pathLen == str.length) return true;
-    if (r < 0 || r >= rows || c < 0 || c >= cols
-            || matrix[r][c] != str[pathLen] || marked[r][c]) {
+        if (pathLen == pathList.length) return true;
+        if (r < 0 || r >= rows || c < 0 || c >= cols
+                || matrix[r][c] != pathList[pathLen] || marked[r][c]) {
 
+            return false;
+        }
+        marked[r][c] = true;
+        for (int[] n : next)
+            if (backtracking(matrix, pathList, marked, pathLen + 1, r + n[0], c + n[1]))
+                return true;
+        marked[r][c] = false;
         return false;
     }
-    marked[r][c] = true;
-    for (int[] n : next)
-        if (backtracking(matrix, str, marked, pathLen + 1, r + n[0], c + n[1]))
-            return true;
-    marked[r][c] = false;
-    return false;
-}
 
-private char[][] buildMatrix(char[] array) {
-    char[][] matrix = new char[rows][cols];
-    for (int r = 0, idx = 0; r < rows; r++)
-        for (int c = 0; c < cols; c++)
-            matrix[r][c] = array[idx++];
-    return matrix;
+    private char[][] buildMatrix(char[] array) {
+        char[][] matrix = new char[rows][cols];
+        for (int r = 0, idx = 0; r < rows; r++)
+            for (int c = 0; c < cols; c++)
+                matrix[r][c] = array[idx++];
+        return matrix;
+    }
+
+    public static void main(String[] args) {
+        Solution solution = new Solution();
+        String val = "ABCESFCSADEE";
+        int rows = 3;
+        int cols = 4;
+        String path = "ABCCED";
+        boolean res = solution.hasPath(val, rows, cols, path);
+        System.out.println(res);
+    }
 }
 ```
diff --git "a/notes/13. \346\234\272\345\231\250\344\272\272\347\232\204\350\277\220\345\212\250\350\214\203\345\233\264.md" "b/notes/13. \346\234\272\345\231\250\344\272\272\347\232\204\350\277\220\345\212\250\350\214\203\345\233\264.md"
index 766b1bd64b2f57730cb43b490df00c4e91513de8..dd96086ed2a9276e312bed3d616a96feac881c6e 100644
--- "a/notes/13. \346\234\272\345\231\250\344\272\272\347\232\204\350\277\220\345\212\250\350\214\203\345\233\264.md"	
+++ "b/notes/13. \346\234\272\345\231\250\344\272\272\347\232\204\350\277\220\345\212\250\350\214\203\345\233\264.md"	
@@ -1,6 +1,6 @@
 # 13. 机器人的运动范围
 
-[NowCoder](https://www.nowcoder.com/practice/6e5207314b5241fb83f2329e89fdecc8?tpId=13&tqId=11219&tPage=1&rp=1&ru=/ta/coding-interviews&qru=/ta/coding-interviews/question-ranking&from=cyc_github)
+[牛客网](https://www.nowcoder.com/practice/6e5207314b5241fb83f2329e89fdecc8?tpId=13&tqId=11219&tPage=1&rp=1&ru=/ta/coding-interviews&qru=/ta/coding-interviews/question-ranking&from=cyc_github)
 
 ## 题目描述
 
diff --git "a/notes/14. \345\211\252\347\273\263\345\255\220.md" "b/notes/14. \345\211\252\347\273\263\345\255\220.md"
index 16ca2493af554ce8cdd379198c77c4cf387ce30b..9108b6353673d3371e0a8d1daca7bd05f153ac67 100644
--- "a/notes/14. \345\211\252\347\273\263\345\255\220.md"	
+++ "b/notes/14. \345\211\252\347\273\263\345\255\220.md"	
@@ -2,7 +2,7 @@
 
 ## 题目链接
 
-[Leetcode](https://leetcode.com/problems/integer-break/description/)
+[牛客网](https://www.nowcoder.com/practice/57d85990ba5b440ab888fc72b0751bf8?tpId=13&tqId=33257&tab=answerKey&from=cyc_github)
 
 ## 题目描述
 
@@ -37,7 +37,7 @@ return 36 (10 = 3 + 3 + 4)
 继续拆成更大的绳子可以发现都比拆成 2 和 3 的效果更差，因此我们只考虑将绳子拆成 2 和 3，并且优先拆成 3，当拆到绳子长度 n 等于 4 时，也就是出现 3+1，此时只能拆成 2+2。
 
 ```java
-public int integerBreak(int n) {
+public int cutRope(int n) {
     if (n < 2)
         return 0;
     if (n == 2)
@@ -55,7 +55,7 @@ public int integerBreak(int n) {
 ### 动态规划
 
 ```java
-public int integerBreak(int n) {
+public int cutRope(int n) {
     int[] dp = new int[n + 1];
     dp[1] = 1;
     for (int i = 2; i <= n; i++)
diff --git "a/notes/18.2 \345\210\240\351\231\244\351\223\276\350\241\250\344\270\255\351\207\215\345\244\215\347\232\204\347\273\223\347\202\271.md" "b/notes/18.2 \345\210\240\351\231\244\351\223\276\350\241\250\344\270\255\351\207\215\345\244\215\347\232\204\347\273\223\347\202\271.md"
index 57e247bfbbfe19461772ce8e66cfc9bb5d2b2a58..5d1f871ba8394397815b28eb22ffd55aa20a9c15 100644
--- "a/notes/18.2 \345\210\240\351\231\244\351\223\276\350\241\250\344\270\255\351\207\215\345\244\215\347\232\204\347\273\223\347\202\271.md"	
+++ "b/notes/18.2 \345\210\240\351\231\244\351\223\276\350\241\250\344\270\255\351\207\215\345\244\215\347\232\204\347\273\223\347\202\271.md"	
@@ -1,6 +1,6 @@
 # 18.2 删除链表中重复的结点
 
-[NowCoder](https://www.nowcoder.com/practice/fc533c45b73a41b0b44ccba763f866ef?tpId=13&tqId=11209&tPage=1&rp=1&ru=/ta/coding-interviews&qru=/ta/coding-interviews/question-ranking&from=cyc_github)
+[牛客网](https://www.nowcoder.com/practice/fc533c45b73a41b0b44ccba763f866ef?tpId=13&tqId=11209&tPage=1&rp=1&ru=/ta/coding-interviews&qru=/ta/coding-interviews/question-ranking&from=cyc_github)
 
 ## 题目描述
 
diff --git "a/notes/19. \346\255\243\345\210\231\350\241\250\350\276\276\345\274\217\345\214\271\351\205\215.md" "b/notes/19. \346\255\243\345\210\231\350\241\250\350\276\276\345\274\217\345\214\271\351\205\215.md"
index 97de47d7b620a6b3fab57ed987508af3d401b0d3..a0ad0053b2bb9ebf717726d3f7b00a3984fe73e4 100644
--- "a/notes/19. \346\255\243\345\210\231\350\241\250\350\276\276\345\274\217\345\214\271\351\205\215.md"	
+++ "b/notes/19. \346\255\243\345\210\231\350\241\250\350\276\276\345\274\217\345\214\271\351\205\215.md"	
@@ -1,6 +1,6 @@
 # 19. 正则表达式匹配
 
-[NowCoder](https://www.nowcoder.com/practice/45327ae22b7b413ea21df13ee7d6429c?tpId=13&tqId=11205&tPage=1&rp=1&ru=/ta/coding-interviews&qru=/ta/coding-interviews/question-ranking&from=cyc_github)
+[牛客网](https://www.nowcoder.com/practice/28970c15befb4ff3a264189087b99ad4?tpId=13&tqId=11205&tab=answerKey&from=cyc_github)
 
 ## 题目描述
 
@@ -13,22 +13,22 @@
 应该注意到，'.' 是用来当做一个任意字符，而 '\*' 是用来重复前面的字符。这两个的作用不同，不能把 '.' 的作用和 '\*' 进行类比，从而把它当成重复前面字符一次。
 
 ```java
-public boolean match(char[] str, char[] pattern) {
+public boolean match(String str, String pattern) {
 
-    int m = str.length, n = pattern.length;
+    int m = str.length(), n = pattern.length();
     boolean[][] dp = new boolean[m + 1][n + 1];
 
     dp[0][0] = true;
     for (int i = 1; i <= n; i++)
-        if (pattern[i - 1] == '*')
+        if (pattern.charAt(i - 1) == '*')
             dp[0][i] = dp[0][i - 2];
 
     for (int i = 1; i <= m; i++)
         for (int j = 1; j <= n; j++)
-            if (str[i - 1] == pattern[j - 1] || pattern[j - 1] == '.')
+            if (str.charAt(i - 1) == pattern.charAt(j - 1) || pattern.charAt(j - 1) == '.')
                 dp[i][j] = dp[i - 1][j - 1];
-            else if (pattern[j - 1] == '*')
-                if (pattern[j - 2] == str[i - 1] || pattern[j - 2] == '.') {
+            else if (pattern.charAt(j - 1) == '*')
+                if (pattern.charAt(j - 2) == str.charAt(i - 1) || pattern.charAt(j - 2) == '.') {
                     dp[i][j] |= dp[i][j - 1]; // a* counts as single a
                     dp[i][j] |= dp[i - 1][j]; // a* counts as multiple a
                     dp[i][j] |= dp[i][j - 2]; // a* counts as empty
diff --git "a/notes/20. \350\241\250\347\244\272\346\225\260\345\200\274\347\232\204\345\255\227\347\254\246\344\270\262.md" "b/notes/20. \350\241\250\347\244\272\346\225\260\345\200\274\347\232\204\345\255\227\347\254\246\344\270\262.md"
index c03369bafea236b6452a1b92462a638c1cf2ed3f..da4b4bf685fd2d91d8e22a624a1522779cd677a6 100644
--- "a/notes/20. \350\241\250\347\244\272\346\225\260\345\200\274\347\232\204\345\255\227\347\254\246\344\270\262.md"	
+++ "b/notes/20. \350\241\250\347\244\272\346\225\260\345\200\274\347\232\204\345\255\227\347\254\246\344\270\262.md"	
@@ -1,6 +1,6 @@
 # 20. 表示数值的字符串
 
-[NowCoder](https://www.nowcoder.com/practice/6f8c901d091949a5837e24bb82a731f2?tpId=13&tqId=11206&tPage=1&rp=1&ru=/ta/coding-interviews&qru=/ta/coding-interviews/question-ranking&from=cyc_github)
+[牛客网](https://www.nowcoder.com/practice/e69148f8528c4039ad89bb2546fd4ff8?tpId=13&tqId=11206&tab=answerKey&from=cyc_github)
 
 ## 题目描述
 
@@ -41,8 +41,8 @@ false
 ```
 
 ```java
-public boolean isNumeric(char[] str) {
-    if (str == null || str.length == 0)
+public boolean isNumeric (String str) {
+    if (str == null || str.length() == 0)
         return false;
     return new String(str).matches("[+-]?\\d*(\\.\\d+)?([eE][+-]?\\d+)?");
 }
diff --git "a/notes/21. \350\260\203\346\225\264\346\225\260\347\273\204\351\241\272\345\272\217\344\275\277\345\245\207\346\225\260\344\275\215\344\272\216\345\201\266\346\225\260\345\211\215\351\235\242.md" "b/notes/21. \350\260\203\346\225\264\346\225\260\347\273\204\351\241\272\345\272\217\344\275\277\345\245\207\346\225\260\344\275\215\344\272\216\345\201\266\346\225\260\345\211\215\351\235\242.md"
index 7b2e1699da4e1b55c2037e525bfba28eedfd25d9..13ca98e5c7a6f2cc70d337bde46e9ba9912f15a6 100644
--- "a/notes/21. \350\260\203\346\225\264\346\225\260\347\273\204\351\241\272\345\272\217\344\275\277\345\245\207\346\225\260\344\275\215\344\272\216\345\201\266\346\225\260\345\211\215\351\235\242.md"	
+++ "b/notes/21. \350\260\203\346\225\264\346\225\260\347\273\204\351\241\272\345\272\217\344\275\277\345\245\207\346\225\260\344\275\215\344\272\216\345\201\266\346\225\260\345\211\215\351\235\242.md"	
@@ -2,7 +2,7 @@
 
 ## 题目链接
 
-[牛客网](https://www.nowcoder.com/practice/beb5aa231adc45b2a5dcc5b62c93f593?tpId=13&tqId=11166&tPage=1&rp=1&ru=/ta/coding-interviews&qru=/ta/coding-interviews/question-ranking&from=cyc_github)
+[牛客网](https://www.nowcoder.com/practice/ef1f53ef31ca408cada5093c8780f44b?tpId=13&tqId=11166&tab=answerKey&from=cyc_github)
 
 ## 题目描述
 
@@ -15,7 +15,7 @@
 方法一：创建一个新数组，时间复杂度 O(N)，空间复杂度 O(N)。
 
 ```java
-public void reOrderArray(int[] nums) {
+public int[] reOrderArray (int[] nums) {
     // 奇数个数
     int oddCnt = 0;
     for (int x : nums)
@@ -29,6 +29,7 @@ public void reOrderArray(int[] nums) {
         else
             nums[j++] = num;
     }
+    return nums;
 }
 
 private boolean isEven(int x) {
@@ -39,7 +40,7 @@ private boolean isEven(int x) {
 方法二：使用冒泡思想，每次都将当前偶数上浮到当前最右边。时间复杂度 O(N<sup>2</sup>)，空间复杂度 O(1)，时间换空间。
 
 ```java
-public void reOrderArray(int[] nums) {
+public int[] reOrderArray(int[] nums) {
     int N = nums.length;
     for (int i = N - 1; i > 0; i--) {
         for (int j = 0; j < i; j++) {
@@ -48,6 +49,7 @@ public void reOrderArray(int[] nums) {
             }
         }
     }
+    return nums;
 }
 
 private boolean isEven(int x) {
diff --git "a/notes/22. \351\223\276\350\241\250\344\270\255\345\200\222\346\225\260\347\254\254 K \344\270\252\347\273\223\347\202\271.md" "b/notes/22. \351\223\276\350\241\250\344\270\255\345\200\222\346\225\260\347\254\254 K \344\270\252\347\273\223\347\202\271.md"
index f77964e7fd4cb5db5db7613399b58e5fa784ec4a..aa00d274af269b4e111eb5792a84da2145cb573d 100644
--- "a/notes/22. \351\223\276\350\241\250\344\270\255\345\200\222\346\225\260\347\254\254 K \344\270\252\347\273\223\347\202\271.md"	
+++ "b/notes/22. \351\223\276\350\241\250\344\270\255\345\200\222\346\225\260\347\254\254 K \344\270\252\347\273\223\347\202\271.md"	
@@ -1,6 +1,6 @@
 # 22. 链表中倒数第 K 个结点
 
-[NowCoder](https://www.nowcoder.com/practice/529d3ae5a407492994ad2a246518148a?tpId=13&tqId=11167&tPage=1&rp=1&ru=/ta/coding-interviews&qru=/ta/coding-interviews/question-ranking&from=cyc_github)
+[牛客网](https://www.nowcoder.com/practice/886370fe658f41b498d40fb34ae76ff9?tpId=13&tqId=11167&tab=answerKey&from=cyc_github)
 
 ## 解题思路
 
diff --git "a/notes/27. \344\272\214\345\217\211\346\240\221\347\232\204\351\225\234\345\203\217.md" "b/notes/27. \344\272\214\345\217\211\346\240\221\347\232\204\351\225\234\345\203\217.md"
index f9ca746a503e5701639ff403b90e425f1c9432b1..18b5f0fa1886dcc5ad269004cabf11bbbd5e5396 100644
--- "a/notes/27. \344\272\214\345\217\211\346\240\221\347\232\204\351\225\234\345\203\217.md"	
+++ "b/notes/27. \344\272\214\345\217\211\346\240\221\347\232\204\351\225\234\345\203\217.md"	
@@ -1,6 +1,6 @@
 # 27. 二叉树的镜像
 
-[NowCoder](https://www.nowcoder.com/practice/564f4c26aa584921bc75623e48ca3011?tpId=13&tqId=11171&tPage=1&rp=1&ru=/ta/coding-interviews&qru=/ta/coding-interviews/question-ranking&from=cyc_github)
+[牛客网](https://www.nowcoder.com/practice/a9d0ecbacef9410ca97463e4a5c83be7?tpId=13&tqId=11171&tab=answerKey&from=cyc_github)
 
 ## 题目描述
 
@@ -9,12 +9,13 @@
 ## 解题思路
 
 ```java
-public void Mirror(TreeNode root) {
+public TreeNode Mirror(TreeNode root) {
     if (root == null)
-        return;
+        return root;
     swap(root);
     Mirror(root.left);
     Mirror(root.right);
+    return root;
 }
 
 private void swap(TreeNode root) {
diff --git "a/notes/5. \346\233\277\346\215\242\347\251\272\346\240\274.md" "b/notes/5. \346\233\277\346\215\242\347\251\272\346\240\274.md"
index 211ae0c6a339a81f734dc887761c316eef93b17f..bd8086161c4e3dcff019bbb02b4c241f0245a29c 100644
--- "a/notes/5. \346\233\277\346\215\242\347\251\272\346\240\274.md"	
+++ "b/notes/5. \346\233\277\346\215\242\347\251\272\346\240\274.md"	
@@ -2,7 +2,7 @@
 
 ## 题目链接
 
-[牛客网](https://www.nowcoder.com/practice/4060ac7e3e404ad1a894ef3e17650423?tpId=13&tqId=11155&tPage=1&rp=1&ru=/ta/coding-interviews&qru=/ta/coding-interviews/question-ranking&from=cyc_github)
+[牛客网](https://www.nowcoder.com/practice/0e26e5551f2b489b9f58bc83aa4b6c68?tpId=13&tqId=11155&tab=answerKey&from=cyc_github)
 
 ## 题目描述
 
diff --git "a/notes/56. \346\225\260\347\273\204\344\270\255\345\217\252\345\207\272\347\216\260\344\270\200\346\254\241\347\232\204\346\225\260\345\255\227.md" "b/notes/56. \346\225\260\347\273\204\344\270\255\345\217\252\345\207\272\347\216\260\344\270\200\346\254\241\347\232\204\346\225\260\345\255\227.md"
index 21c1c3dc779562d5326da21efe5b12b4545ce1bd..4ab74ad3c3e29d0915e9c7cfd4c5d8b8849034fb 100644
--- "a/notes/56. \346\225\260\347\273\204\344\270\255\345\217\252\345\207\272\347\216\260\344\270\200\346\254\241\347\232\204\346\225\260\345\255\227.md"	
+++ "b/notes/56. \346\225\260\347\273\204\344\270\255\345\217\252\345\207\272\347\216\260\344\270\200\346\254\241\347\232\204\346\225\260\345\255\227.md"	
@@ -2,7 +2,7 @@
 
 ## 题目链接
 
-[牛客网](https://www.nowcoder.com/practice/e02fdb54d7524710a7d664d082bb7811?tpId=13&tqId=11193&tPage=1&rp=1&ru=/ta/coding-interviews&qru=/ta/coding-interviews/question-ranking&from=cyc_github)
+[牛客网](https://www.nowcoder.com/practice/389fc1c3d3be4479a154f63f495abff8?tpId=13&tqId=11193&tab=answerKey&from=cyc_github)
 
 ## 题目描述
 
@@ -19,16 +19,27 @@
 下面的解法中，num1 和 num2 数组的第一个元素是用来保持返回值的... 实际开发中不推荐这种返回值的方式。
 
 ```java
-public void FindNumsAppearOnce(int[] nums, int num1[], int num2[]) {
+public int[] FindNumsAppearOnce (int[] nums) {
+    int[] res = new int[2];
     int diff = 0;
     for (int num : nums)
         diff ^= num;
     diff &= -diff;
     for (int num : nums) {
         if ((num & diff) == 0)
-            num1[0] ^= num;
+            res[0] ^= num;
         else
-            num2[0] ^= num;
+            res[1] ^= num;
     }
+    if (res[0] > res[1]) {
+        swap(res);
+    }
+    return res;
+}
+
+private void swap(int[] nums) {
+    int t = nums[0];
+    nums[0] = nums[1];
+    nums[1] = t;
 }
 ```