Checks whether an array of points forms a square. License: MIT

CheckIfPointsMakeSquare.cs

using System;
using System.Drawing;

/// <summary>
/// Checks whether an array of <see cref="Point"/> forms a square.
/// </summary>
/// <param name="points">The points to check.</param>
private static bool CheckIfPointsMakeSquare(Point[] points)
{
  if (points == null) { throw new ArgumentNullException(nameof(points)); }
  // Cannot be square if there aren't four points
  if (points.Length != 4) { return false; }

  // Takes two points, returns distance squared (to avoid sqrt and floating point precision errors)
  Func<Point, Point, int> distSquared = (p1, p2) => (int)Math.Pow(p2.X - p1.X, 2) + (int)Math.Pow(p2.Y - p1.Y, 2);

  // Calculate the squared distance of the first side
  int firstDist = distSquared(points[3], points[0]);
  // Compare the squared distances of the other three sides with the first side. Return false if not equal.
  for (var i = 0; i < 3; i++) { if (distSquared(points[i], points[i + 1]) != firstDist) { return false; } }
  // Compare the two diagonal distances. Return false if not equal.
  if (distSquared(points[0], points[2]) != distSquared(points[1], points[3])) { return false; }
  // Four sides and two diagonals are equal, return true
  return true;
}