Sum Root to Leaf Numbers深度优先计算路径和

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.

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/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
private:
    int sum;
public:
    void dfs(TreeNode *root,int num){
        if(root==NULL)
            return;
        if(root->left==NULL && root->right==NULL){
            num=num*10+root->val;
            sum=sum+num;
            return;
        }
        num=num*10+root->val;
        dfs(root->left,num);
        dfs(root->right,num);
    }
    int sumNumbers(TreeNode *root) {
        sum=0;
        dfs(root,0);
        return sum;
            
    }
};