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.

 top-down 显然很直接.  可以改变每个node的值. 如果不想改变可以添加一个path.在函数参数里.

/** * Definition for binary tree * public class TreeNode { *     int val; *     TreeNode left; *     TreeNode right; *     TreeNode(int x) { val = x; } * } */public class Solution {    public int sumNumbers(TreeNode root) {                int[] result = {0};        int path = 0;        GenerateSum(root,result,path);        return result[0];    }   void GenerateSum(TreeNode root, int[] result, int path){        if(root == null){            return;        }        path = path*10 + root.val;        if(root.left == null && root.right == null){            result[0] += path;            return;        }                        GenerateSum(root.left,result,path);        GenerateSum(root.right,result,path);   }}