Create 257. Binary Tree Paths.md

257. Binary Tree Paths.md

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+# [257. Binary Tree Paths](https://leetcode.com/problems/binary-tree-paths/description/)
+# 思路
+递归算法，用一个curr_path记录当前的path，每当遇到叶子节点时就将curr_path push到一个字符串数组里。
+
+# C++
+``` C++
+class Solution {
+private:
+    vector<string>res;
+    string curr_path;
+    void find_leaf(TreeNode* root){
+        if(root == NULL) return;
+        if(!curr_path.empty()) curr_path += "->"; // 不是第一个数，应该先加上“->”
+        curr_path += (to_string(root -> val));
+        
+        if(root -> right == NULL && root -> left == NULL) res.push_back(curr_path);
+        
+        find_leaf(root -> left);
+        find_leaf(root -> right);
+        
+        // 将当前节点从curr_path中删掉,注意可能是负数所以不能用“-”作为箭头的标志
+        while(!curr_path.empty() && curr_path[curr_path.size()-1] != '>'){ // 删除最后一个字符直到curr_path空了或者遇到箭头的标志">"
+            curr_path.erase(curr_path.end() - 1);
+        }
+        if(!curr_path.empty()) curr_path.erase(curr_path.size() - 2, 2); // 删除末尾的"->"
+    }
+public:
+    vector<string> binaryTreePaths(TreeNode* root) {
+        find_leaf(root);
+        return res;
+    }
+};
+```