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.
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.
思想： 分三种情况： 1. 当前结点为空，返回0. 2. 叶子结点， 返回当前值. 3. 父结点，返回左右两个 path 值的和。
/**
* Definition for binary tree
* struct TreeNode {
* int val;
* TreeNode *left;
* TreeNode *right;
* TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
int dfs(TreeNode *root, int sum) {
if(root == 0) return 0;
sum = sum * 10 + root->val;
if(root->left || root->right)
return dfs(root->left, sum) + dfs(root->right, sum);
return sum;
}
class Solution {
public:
int sumNumbers(TreeNode *root) {
return dfs(root, 0);
}
};