Add a solution to Detect Squares

Author: soapyigu

Design/DetectSquares.swift

@@ -0,0 +1,60 @@
+/**
+ * Question Link: https://leetcode.com/problems/detect-squares/
+ * Primary idea: Use hashmap to track points having the same x and y and calculate all possible results
+ *
+ * Time Complexity: add - O(1), count - O(n)
+ * Space Complexity: O(n)
+ *
+ */
+
+class DetectSquares {
+    
+    private var xPoints = [Int: [Int: Int]]()
+    private var yPoints = [Int: [Int: Int]]()
+
+    init() { }
+    
+    func add(_ point: [Int]) {
+        let x = point[0], y = point[1]
+        
+        xPoints[x, default: [y: 0]][y, default: 0] += 1
+        yPoints[y, default: [x: 0]][x, default: 0] += 1
+    }
+    
+    func count(_ point: [Int]) -> Int {
+        let x = point[0], y = point[1]
+        
+        guard let xEqualPoints = xPoints[x], let yEqualPoints = yPoints[y] else {
+            return 0
+        }
+        
+        var res = 0
+        
+        for (yEqualPointX, firstPointsCount) in yEqualPoints {
+            if x == yEqualPointX {
+                continue
+            }
+            let sideLength = abs(x - yEqualPointX)
+            // check bottom square
+			if let secondPointCount = xEqualPoints[y - sideLength] {
+				if let thirdPointCount = xPoints[yEqualPointX]?[y - sideLength] {
+					res += firstPointsCount * secondPointCount * thirdPointCount
+				}
+			}
+            if let secondPointCount = xEqualPoints[y + sideLength] {
+				if let thirdPointCount = xPoints[yEqualPointX]?[y + sideLength] {
+					res += firstPointsCount * secondPointCount * thirdPointCount
+				}
+			}
+        }
+        
+        return res
+    }
+}
+
+/**
+ * Your DetectSquares object will be instantiated and called as such:
+ * let obj = DetectSquares()
+ * obj.add(point)
+ * let ret_2: Int = obj.count(point)
+ */