[LeetCode] 113: Sum Root to Leaf Numbers

[Problem]

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.

[Solution]

/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
vector<int> generatePaths(TreeNode *root, int preVal){
vector<int> res;
if(root == NULL){
return res;
}
else if(root->left == NULL && root->right == NULL){
res.push_back(preVal*10 + root->val);
}
else{
vector<int> left = generatePaths(root->left, preVal*10 + root->val);
vector<int> right = generatePaths(root->right, preVal*10 + root->val);
for(int i = 0; i < left.size(); ++i){
res.push_back(left[i]);
}
for(int i = 0; i < right.size(); ++i){
res.push_back(right[i]);
}
}

return res;
}
int sumNumbers(TreeNode *root) {
// Note: The Solution object is instantiated only once and is reused by each test case.
vector<int> paths = generatePaths(root, 0);
int res = 0;
for(int i = 0; i < paths.size(); ++i){
res += paths[i];
}
return res;
}
};

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