Sum Root to Leaf Numbers

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.

題目：從根到葉子表示一個數字，求一棵樹中所有值的和。

分析：先序遍歷，碰到葉子節點，將當前的值加到res上，否則，繼續乘10相加。

代碼：

/**
 * 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) {
        int num=0;
        if(root==NULL) return 0;
        sum(root,num);
        return res;
    }
    void sum(TreeNode *root, int num){//這裏num不要用 引用！！！
        if(root==NULL) return;
        num=num*10+root->val;
        if(root->left==NULL && root->right==NULL){//如果達到了葉子節點
            res=res+num;
        }
        
        sum(root->left,num);
        sum(root->right,num);
       
    }
    
private:
    int res=0;
};