Leetcode-473. Matchsticks to Square

前言：为了后续的实习面试，开始疯狂刷题，非常欢迎志同道合的朋友一起交流。因为时间比较紧张，目前的规划是先过一遍，写出能想到的最优算法，第二遍再考虑最优或者较优的方法。如有错误欢迎指正。博主首发CSDN，mcf171专栏。

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Remember the story of Little Match Girl? By now, you know exactly what matchsticks the little match girl has, please find out a way you can make one square by using up all those matchsticks. You should not break any stick, but you can link them up, and each matchstick must be used exactly one time.

Your input will be several matchsticks the girl has, represented with their stick length. Your output will either be true or false, to represent whether you could make one square using all the matchsticks the little match girl has.

Example 1:

Input: [1,1,2,2,2]Output: trueExplanation: You can form a square with length 2, one side of the square came two sticks with length 1.

Example 2:

Input: [3,3,3,3,4]Output: falseExplanation: You cannot find a way to form a square with all the matchsticks.

Note:

1. The length sum of the given matchsticks is in the range of 0 to 10^9.
2. The length of the given matchstick array will not exceed 15.

这个题目当时比赛的时候没做出来，原因有两个，一个是题目看错了，我以为是从中选出一部分能组成矩阵，原来是所有的火柴棍，其次总想着有没有简单的方法，导致没做出来，应该先用暴力吧题目解出来的。Your runtime beats 60.86% of java submissions.

public class Solution {    public boolean makesquare(int[] nums) {        if(nums.length < 4 ) return false;        int edge = 0;        for(int item : nums) edge += item;        if(edge % 4 != 0) return false;        edge = edge / 4;        Arrays.sort(nums);        return match(new int[4],nums, nums.length - 1, edge);    }    public boolean match(int[] sum, int[] nums, int index, int target){if(index == - 1){if(sum[0] == target && sum[1] == target && sum[2] == target && sum[3] ==target){return true;}return false;}for(int i = 0; i < 4; i ++){if(sum[i] + nums[index] <= target){sum[i] += nums[index];if(match(sum,nums,index - 1, target)) return true;sum[i] -= nums[index];}}return false;    }}