Binary Tree Paths

Given a binary tree, return all root-to-leaf paths.

For example, given the following binary tree:

   1
 /   
2     3
 
  5

All root-to-leaf paths are:

["1->2->5", "1->3"]

Analyse: Recursion.

Runtime: 4ms.

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    vector<string> binaryTreePaths(TreeNode* root) {
        vector<string> result;
        if(!root) return result;
        
        dfs(root, result, "");
        return result;
    }
    void dfs(TreeNode* root, vector<string>& result, string temp){
        if(!root) return;
        
        temp = temp + std::to_string(root->val);
        if(root->left) dfs(root->left, result, temp + "->");
        if(root->right) dfs(root->right, result, temp + "->");
        if(!root->left && !root->right) result.push_back(temp);
    }
    /*string i2a(int val){
        if(val == 0) return "0";
        
        string result;
        if(val < 0){
            result += "-";
            val = -val;
        }
        while(val){
            result += val % 10 + '0';
            val /= 10;
        }
        int i = 0;
        if(result[0] = '-') i = 1;
        for(int j = result.length() - 1; i <= j; i++, j--){
            swap(result[i], result[j]);
        }
        return result;
    }*/
};