LeetCode 129. Sum Root to Leaf Numbers

iven 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.

这是一道树的遍历问题，采用递归解决就行了。

/** * Definition for a binary tree node. * public class TreeNode { *     int val; *     TreeNode left; *     TreeNode right; *     TreeNode(int x) { val = x; } * } */public class Solution {    private int helper(TreeNode root, int val, int sum){        if(root == null){            return sum;        }                int curVal = val*10+root.val;        if(root.left == null && root.right == null){            sum += curVal;            return sum;        }        sum = helper(root.left,curVal, sum );        sum = helper(root.right, curVal, sum);        return sum;    }    public int sumNumbers(TreeNode root) {        return helper(root, 0, 0);    }}

时间复杂度O(N)。