add 299

README.md

@@ -223,6 +223,7 @@ My LeetCode solutions with Chinese explanation. 我的LeetCode中文题解。
 | 292 |[Nim Game](https://leetcode.com/problems/nim-game)|[C++](https://github.com/ShusenTang/LeetCode/blob/master/solutions/292.%20Nim%20Game.md)|Easy|  |
 | 295 |[Find Median from Data Stream](https://leetcode.com/problems/find-median-from-data-stream/)|[C++](solutions/295.%20Find%20Median%20from%20Data%20Stream.md)|Hard|  |
 | 297 |[Serialize and Deserialize Binary Tree](https://leetcode.com/problems/serialize-and-deserialize-binary-tree/)|[C++](solutions/297.%20Serialize%20and%20Deserialize%20Binary%20Tree.md)|Hard|  |
+| 299 |[Bulls and Cows](https://leetcode.com/problems/bulls-and-cows/)|[C++](solutions/299.%20Bulls%20and%20Cows.md)|Medium|  |
 | 300 |[Longest Increasing Subsequence](https://leetcode.com/problems/longest-increasing-subsequence/)|[C++](https://github.com/ShusenTang/LeetCode/blob/master/solutions/300.%20Longest%20Increasing%20Subsequence.md)|Medium|  |
 | 301 |[Remove Invalid Parentheses](https://leetcode.com/problems/remove-invalid-parentheses/)|[C++](solutions/301.%20Remove%20Invalid%20Parentheses.md)|Hard|  |
 | 303 |[Range Sum Query - Immutable](https://leetcode.com/problems/range-sum-query-immutable)|[C++](https://github.com/ShusenTang/LeetCode/blob/master/solutions/303.%20Range%20Sum%20Query%20-%20Immutable.md)|Easy|  |

solutions/299. Bulls and Cows.md

@@ -0,0 +1,55 @@
+# [299. Bulls and Cows](https://leetcode.com/problems/bulls-and-cows/)
+
+# 思路
+A的个数比较简单，只需要挨个位置比较即可。B的个数，需要先用一个数组记录secret中各数字出现的个数（需排除A情况），再遍历一遍看guess中的数字是否在secret中出现过，若是，则B个数加一。
+
+
+# C++
+
+
+```C++
+class Solution {
+public:
+    string getHint(string secret, string guess) {
+        int a = 0, b = 0;
+        vector<int>mp(10, 0);
+        for(int i = 0; i < secret.size(); i++){
+            if(secret[i] != guess[i]) mp[secret[i] - '0']++;
+        }
+        for(int i = 0; i < secret.size(); i++){
+            if(secret[i] == guess[i]) a++;
+            else if(mp[guess[i] - '0'] > 0){
+                b++;
+                mp[guess[i] - '0']--;
+            }
+        }
+        
+        return to_string(a) + "A" + to_string(b) + "B";
+    }
+};
+```
+也可以只遍历一遍：
+```C++
+class Solution {
+public:
+    string getHint(string secret, string guess) {
+        int a = 0, b = 0;
+        vector<int>mp1(10, 0);
+        vector<int>mp2(10, 0);
+        for(int i = 0; i < secret.size(); i++){
+            if(secret[i] != guess[i]){
+                mp1[secret[i] - '0']++;
+                mp2[guess[i] - '0']++;
+            }else{
+                a++;
+            }
+
+        }
+        for(int i = 0; i < 10; i++){
+            b += min(mp1[i], mp2[i]);
+        }
+        
+        return to_string(a) + "A" + to_string(b) + "B";
+    }
+};
+```