Valid Square

Given the coordinates of four points in 2D space, return whether the four points could construct a square.

The coordinate (x,y) of a point is represented by an integer array with two integers.

Example:

Input: p1 = [0,0], p2 = [1,1], p3 = [1,0], p4 = [0,1]
Output: True

Note: 

1. All the input integers are in the range [-10000, 10000].
2. A valid square has four equal sides with positive length and four equal angles (90-degree angles).
3. Input points have no order.

分析：

如果四个点两两之间的距离满足：1）存在四个边段距离相等 2）存在两个对角线距离相等。则构成四边形。

注意：在求点距离的时候需要注意是否存在整数溢出，由于给定范围是[-10000,10000],最大值不会超过2^32 -1，因此不用担心

代码：

class Solution {public boolean validSquare(int[] p1, int[] p2, int[] p3, int[] p4) {int[] d = new int[6];d[0] = distance(p1, p2);d[1] = distance(p1, p3);d[2] = distance(p1, p4);d[3] = distance(p2, p3);d[4] = distance(p2, p4);d[5] = distance(p3, p4);Arrays.sort(d);return d[0] == d[3] && d[3]<d[4] && d[4] == d[5];}private int distance(int[] p1, int[] p2) {int x = Math.abs(p1[0] - p2[0]);int y = Math.abs(p1[1] - p2[1]);return x * x + y * y;}
}