leetcode-129 Sum Root to Leaf Numbers

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DFS的题目好像都是用递归

遇到递归的时候，把终止条件，各种条件想清楚就可以大胆写了，可以先举几个简单的例子帮助

<span style="font-family:Microsoft YaHei;font-size:14px;">/*** Definition for binary tree* struct TreeNode {*     int val;*     TreeNode *left;*     TreeNode *right;*     TreeNode(int x) : val(x), left(NULL), right(NULL) {}* };*/
class Solution {
public:int sumNumbers(TreeNode *root) {if(root == NULL) return 0;int sum = 0;return helper(root,sum);}int helper(TreeNode *node,int sum){if(node->left == NULL && node->right == NULL)return sum * 10 + node->val;int val = 0;if(node->left != NULL)val += helper(node->left,sum * 10 + node->val);if(node->right != NULL)val += helper(node->right,sum * 10 + node->val);return val;}
};</span>

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