LeetCode-129. 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.

Note:A leaf is a node with no children.

Example:

Input: [1,2,3]
    1
   / \
  2   3
Output: 25
Explanation:
The root-to-leaf path 1->2 represents the number 12.
The root-to-leaf path 1->3 represents the number 13.
Therefore, sum = 12 + 13 = 25.

Example 2:

Input: [4,9,0,5,1]
    4
   / \
  9   0
 / \
5   1
Output: 1026
Explanation:
The root-to-leaf path 4->9->5 represents the number 495.
The root-to-leaf path 4->9->1 represents the number 491.
The root-to-leaf path 4->0 represents the number 40.
Therefore, sum = 495 + 491 + 40 = 1026.

题解：

class Solution {
public:
    int sums (TreeNode *root, int val) {
        if (root == NULL) {
            return 0;
        }
        if (root->left == NULL && root->right == NULL) {
            return root->val + val * 10;
        }
        root->val = root->val + val * 10;
        return sums(root->left, root->val) + sums(root->right, root->val);
    }
    int sumNumbers(TreeNode* root) {
        return sums(root, 0);
    }
};