leetcode 593. Valid Square | 593. 有效的正方形（Java）

深藏阁楼爱情的钟 2022-09-14 12:29 170阅读 0赞

## 题目 ##

[https://leetcode.com/problems/valid-square/][https_leetcode.com_problems_valid-square]  
![在这里插入图片描述][watermark_type_ZHJvaWRzYW5zZmFsbGJhY2s_shadow_50_text_Q1NETiBA5a-S5rOJSHE_size_20_color_FFFFFF_t_70_g_se_x_16]

## 题解 ##

因为顺序未知，所以可能有四种组合情况。（check时，以四个点顺时针排列为待判断的正方形）

class Solution { 
        public boolean validSquare(int[] p1, int[] p2, int[] p3, int[] p4) { 
            return check(p1, p2, p3, p4) || check(p1, p2, p4, p3) ||
                    check(p1, p3, p2, p4) || check(p1, p3, p4, p2);
        }
    
        public boolean check(int[] A, int[] B, int[] C, int[] D) { 
            if (distance(A, B) != distance(C, D) || distance(A, B) != distance(B, C) ||
                    distance(A, D) != distance(B, C)) return false;
            // AB⊥AD
            double kAB = slope(A, B);
            double kAD = slope(A, D);
            if (kAB == Integer.MAX_VALUE) return kAD == 0;
            if (kAD == Integer.MAX_VALUE) return kAB == 0;
            return kAB * kAD - (-1) < 0.0001;
        }
    
        public int distance(int[] A, int[] B) { 
            return (int) (Math.pow(B[1] - A[1], 2) + Math.pow(B[0] - A[0], 2));
        }
    
        public double slope(int[] A, int[] B) { 
            if (B[0] - A[0] == 0) return Integer.MAX_VALUE; // inf
            else return (double) (B[1] - A[1]) / (B[0] - A[0]);
        }
    }

![在这里插入图片描述][watermark_type_ZHJvaWRzYW5zZmFsbGJhY2s_shadow_50_text_Q1NETiBA5a-S5rOJSHE_size_20_color_FFFFFF_t_70_g_se_x_16 1]

[https_leetcode.com_problems_valid-square]: https://leetcode.com/problems/valid-square/
[watermark_type_ZHJvaWRzYW5zZmFsbGJhY2s_shadow_50_text_Q1NETiBA5a-S5rOJSHE_size_20_color_FFFFFF_t_70_g_se_x_16]: /images/20220828/17bb4a4b43d344518113bbd4ac0af13c.png
[watermark_type_ZHJvaWRzYW5zZmFsbGJhY2s_shadow_50_text_Q1NETiBA5a-S5rOJSHE_size_20_color_FFFFFF_t_70_g_se_x_16 1]: /images/20220828/ed0e174b4c964277bb9d57bb83504eed.png