【LeetCode】【129】【Sum Root to Leaf Numbers】

版权声明：本文为博主原创文章，未经博主允许不得转载。 https://blog.csdn.net/u012503241/article/details/82946829

题目：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.
Example:
Input: [1,2,3]
1
/ \
2 3
Output: 25
Explanation:
The root-to-leaf path 1->2 represents the number 12.
The root-to-leaf path 1->3 represents the number 13.
Therefore, sum = 12 + 13 = 25.
解题思路：简单的递归，用心感受就好，注意写好递归的结束条件
代码：

class TreeNode {
      int val;
      TreeNode left;
      TreeNode right;
      TreeNode(int x) { val = x; }
}
    int ans = 0;
    public int sumNumbers(TreeNode root) {
        sum(root,0);
        return ans;
    }
    public void sum(TreeNode root,int curSum){
        if(root == null) return;
        if(root.left == null && root.right == null)
            ans+= curSum*10+root.val;
        sum(root.left,curSum*10+root.val);
        sum(root.right,curSum*10+root.val);
    }