LC 593. 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.

从边入手，如果四个点不重合，那么形成的四条边加两个对角线只可能有两个情况，且对角线要长。

Runtime: 16 ms, faster than 57.63% of Java online submissions for Valid Square.

class Solution {
  public boolean validSquare(int[] p1, int[] p2, int[] p3, int[] p4) {
    int[][] p = {{p1[0],p1[1]},{p2[0],p2[1]},{p3[0],p3[1]},{p4[0],p4[1]}};
    int cnt = 0;
    int[] len = new int[6];
    for(int i=0; i<4; i++){
      for(int j=i+1; j<4 ;j++){
        if(p[i][0] == p[j][0] && p[i][1] == p[j][1]) return false;
        len[cnt++] = (p[i][0]-p[j][0])*(p[i][0]-p[j][0])+(p[i][1]-p[j][1])*(p[i][1]-p[j][1]);
      }
    }
    Arrays.sort(len);
    if(len[0] == len[2] && len[4] == len[5] && len[4] > len[1]){
      return true;
    }
    return false;
  }
}