129. Sum Root to Leaf Numbers（从根节点加到叶子节点的和, 回溯模板）

 

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.

 

 

class Solution {
public:
    int sum;
    void backtrack(TreeNode* root, int path) {
        if(root == nullptr) return;
        if(root->left == nullptr && root->right == nullptr) {
            path = path * 10 + root->val;
            sum += path;
            return;
        }
        path = path * 10 + root->val;
        backtrack(root->left,path);
        backtrack(root->right,path);
        path = path/10;
    }
    int sumNumbers(TreeNode* root) {
        backtrack(root,0);
        return sum;
    }
};