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LeetCode题目描述

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.

我的思路：

就像之前的找所有根到叶子的路径问题，把所有路径找出来再算，于是写了如下代码

public int sumNumbers(TreeNode root) {        List
   
    
     > res = new ArrayList();        List
     
       list = new ArrayList();        int sum = 0;        go(root,res,list);                for(int i = 0;i < res.size();i++){            List
      
        tem = res.get(i);            int time = 0;            for(int k = tem.size()-1;k >= 0;k--){                int num = tem.get(k);                System.out.println(num);                int ti = time;                while(ti > 0){                    num = num*10;                    ti --;                }                sum += num;                time++;            }        }        return sum;    }    public void go(TreeNode t,List
       
        
         > res,List
         
           list){ if(t == null)return; list.add(t.val); if(t.left==null&&t.right==null){ res.add(list); //System.out.println(res); list.remove(list.size()-1); //System.out.println(res); return; } go(t.left,res,list); go(t.right,res,list); list.remove(list.size()-1); }
         
        
       
      
     
    
   

问题来了

if(t.left==null&&t.right==null){            res.add(list);            //System.out.println(res);            list.remove(list.size()-1);            //System.out.println(res);            return; }

所以改为res.add(new ArrayList(list));相当于复制对象。

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