[leetcode] Sum Root to Leaf Numbers

Given a binary tree containing digits from 0-9 only, each root-to-leaf path could represent a number.

An example is the root-to-leaf path 1->2->3 which represents the number 123.

Find the total sum of all root-to-leaf numbers.

For example,

    1
   / \
  2   3

The root-to-leaf path 1->2 represents the number 12.
The root-to-leaf path 1->3 represents the number 13.

Return the sum = 12 + 13 = 25.

递归咯~ 返回条件就是当前节点为叶子节点，结算一下

/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
    int ret;
public:
    void num(TreeNode *root, int x){
        int v = x* 10 + root -> val;
        if(!root -> left && !root -> right){
            ret += v;
            return;
        }
        if(root -> left) num(root -> left, v);
        if(root -> right) num(root -> right, v);
        
    }

    int sumNumbers(TreeNode *root) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        ret = 0;
        
        if(!root) return 0;
        num(root, 0);
        return ret;
    }
};