[Leetcode-Tree] 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.

1. 解题思路

本题要求所有从根结点到叶子节点的路径和，我们用递归实现。
结束条件：当遇到叶子节点时，直接结束，返回计算好的sum;如果遇到空节点，则返回数值0。

2.代码

public class Solution {
    public int sumNumbers(TreeNode root) {
        return sum(root,0);
    }
    private int sum(TreeNode root, int cur){
        if(root==null) return 0;
        cur=10*cur+root.val;
        if(root.left==null&&root.right==null)
            return cur;
        else
            return sum(root.left,cur)+sum(root.right,cur);
    }
}