129. Sum Root to Leaf Numbers

简单题，递归就ok

/**
 * 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:
    int sum;
    void thesum(TreeNode* root, int n){
        if(root -> left == NULL && root -> right == NULL){
            sum = sum + n * 10 + root -> val;
            return ;
        }
        if(root -> left != NULL) thesum(root -> left, n * 10 + root -> val);
        if(root -> right != NULL) thesum(root -> right, n * 10 + root -> val);

    }
    int sumNumbers(TreeNode* root) {
        if(root == NULL) return 0;
        sum = 0;
        thesum(root, 0);
        return sum;
    }
};