129. Sum Root to Leaf Numbers 注意要和124题对比，都是DFS问题

题目：

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.

代码：

/**
 * 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 ans;
    int sumNumbers(TreeNode* root) {
        int res = 0;
        if(root == NULL) {
            
            return 0;
        }
        sum_depth(root, root->val);
        for(auto it : ans)
        res += it;
        return res;
    }
    int sum_depth(TreeNode* root, int sum){
        
        if(root == NULL) {
            
            return 0;
        }
        if(!root->left && !root->right) {ans.push_back(sum);return 1;}
        int leftH;if(root->left) sum_depth(root->left, sum * 10 + root->left->val);
        int rightH;if(root->right) sum_depth(root->right, sum * 10 + root->right->val);
        return max(leftH, rightH) + 1;
    }
};

Java：

int maxPathSum(TreeNode* root) {
    int maxValue = INT_MIN;
    maxPathDown(root, maxValue);
    return maxValue;
}
int maxPathDown(TreeNode* node, int &maxValue) {
    if (node == nullptr) return 0;
    int left = max(0, maxPathDown(node->left, maxValue));
    int right = max(0, maxPathDown(node->right, maxValue));
    maxValue = max(maxValue, left + right + node->val);
    return max(left, right) + node->val;
}