原题链接在这里：https://leetcode.com/problems/valid-square/
题目：
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:
- All the input integers are in the range [-10000, 10000].
- A valid square has four equal sides with positive length and four equal angles (90-degree angles).
- Input points have no order.
题解：
Sort the 4 points based on x, if x are equal, sort on y. Then find out, p0 - p3, p1 - p2 are always diagonal.
Compare 4 edge length are equal. And compare 2 diagonal legnth are equal.
Time Complexity: O(1).
Space: O(1).
AC Java:
1 class Solution { 2 public boolean validSquare(int[] p1, int[] p2, int[] p3, int[] p4) { 3 int [][] pos = new int[][]{p1, p2, p3, p4}; 4 Arrays.sort(pos, (a, b) -> a[0] == b[0] ? a[1] - b[1] : a[0] - b[0]); 5 return dist(pos[0], pos[1]) != 0 && dist(pos[0], pos[1]) == dist(pos[1], pos[3]) && 6 dist(pos[1], pos[3]) == dist(pos[3], pos[2]) && dist(pos[3], pos[2]) == dist(pos[2], pos[0]) && 7 dist(pos[0], pos[3]) == dist(pos[1], pos[2]); 8 } 9 10 private long dist(int [] a, int [] b){ 11 return (b[0] - a[0]) * (b[0] - a[0]) + (b[1] - a[1]) * (b[1] - a[1]); 12 } 13 }