leetcode-129

leetcode 129

递归解题，将节点值传入参数，随层数每次乘10相加，递归边界为空节点，返回0，对于叶子节点，返回结果和加上叶子值；然后分别递归左子树,右子树相加。

/**
 * 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 sumNumbers(TreeNode* root) {
        return helper(root, 0);
    }

private:
    int helper(TreeNode *root, int ret) {
        if(nullptr == root) return 0;
        if(nullptr == root->left && nullptr == root->right) {
            return ret * 10 +  root->val;
        }
        else if(root->left) helper(root->left, ret * 10 + root->val);
        else if(root->right) helper(root->right, ret * 10 + root->val);
    }
};