Leetcode:Sum Root to Leaf Numbers

URL

https://leetcode.com/problems/sum-root-to-leaf-numbers/description/

描述

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.

解题思路

DFS

代码

int sum = 0;    public int sumNumbers(TreeNode root) {        dfs(root,new StringBuilder());        return sum;    }    void dfs(TreeNode root,StringBuilder strBuilder){        if(root==null) return;        strBuilder.append(root.val);        if(root.left==null&&root.right==null){            sum+=Integer.valueOf(strBuilder.toString());        }        dfs(root.left,strBuilder);        dfs(root.right,strBuilder);        strBuilder.deleteCharAt(strBuilder.length()-1);    }