[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.

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

.

/**
* 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) {
vector<int> res;
if (root == NULL) {
return 0;
}
dfs(root, res, 0);
return accumulate(res.begin(), res.end(), 0);
}
void dfs(TreeNode *root, vector<int> &res, int sum) {
if (root == NULL) {
return ;
}
if (!root->left && !root->right) {
sum = sum*10 + root->val;
res.push_back(sum);
}

sum  = sum*10 + root->val;
dfs(root->left, res, sum);
dfs(root->right, res, sum);
sum = sum/10;
}
};