Sum Root To Leaf Num

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:
    vector<int> path;
    int sum;
    void calcSumNumbers(TreeNode *root,int idx){
        if (!root){
            return;    
        }
        if (path.size() != idx + 1){
            path.resize(idx + 1);
        }
        path[idx++] = root->val;
        if (!root->left && !root->right){
            for(size_t i = 0; i < path.size(); i++){  //从后往前也OK，小心size_t溢出，尤其在逆向循环中
                sum += path[i] *  pow(10,path.size() -i - 1);
            }
            return;
        }
        calcSumNumbers(root->left,idx);
        calcSumNumbers(root->right,idx);
    }
    int sumNumbers(TreeNode *root) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        if (!root){
            return 0;
        }
        sum = 0;
        calcSumNumbers(root,0);
        return sum;
    }
};