1.LeetCode473题目链接

https://leetcode-cn.com/problems/matchsticks-to-square/submissions/

2.解题思路

首先我们将不能组成正方形的结果去除，边长不能整除4的，然后记录正方形变长，递归累加到每个边等于变长，若可以得到四条边则为true。

 public boolean makesquare(int[] nums) {
        int sum = 0;
        for (int num : nums) {
            sum += num;
        }
        if (sum == 0 || sum % 4 != 0) {
            return false;
        }
        int target = sum / 4;
        for (int num : nums) {
            if (num > target) {
                return false;
            }
        }
        //群里同学说现排序效率更高，试了下，提高了40%的效率。。
        Arrays.sort(nums);
        search(nums.length - 1, nums, target, new int[4]);
        return ans;

    }

    boolean ans = false;

    void search(int cur, int[] nums, int target, int[] temp) {
        if (ans){
            return;
        }
        if (cur == -1) {
            for (int num : temp) {
                if (num != target)
                    return;
            }
            ans = true;
            return;
        }
        for (int i = 0; i < temp.length; i++) {
            int last = temp[i];
            temp[i] += nums[cur];
            if (temp[i] <= target) {
                search(cur - 1, nums, target, temp);
            }
            temp[i] = last;
        }
    }