leetcode:Binary Tree Paths

Binary Tree Paths

Given a binary tree, return all root-to-leaf paths.For example, given the following binary tree:

All root-to-leaf paths are:[“1->2->5”, “1->3”]

分析
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class Solution {
public:
    vector<string> binaryTreePaths(TreeNode* root) {
        vector<string> ret;
        string str;
        dfs(ret, str, root);
        return ret;
    }
    void dfs(vector<string>& ret, string& str, TreeNode* root){
        if (!root)
            return;
        if (root && !root->left&&!root->right){
            str+=to_string(root->val);
            ret.push_back(str);
            return;
        }
        string tmp = str;
        str += to_string(root->val)+"->";
        if (root->left)
            dfs(ret, str, root->left);
        str = tmp;

        tmp = str;
        str += to_string(root->val) + "->";
        if (root->right)
            dfs(ret, str, root->right);
        str=tmp;
    }
};