Added checks for subscript and fixed initializer compile error

Author: Deep Parekh

Array2D/Array2D.playground/Contents.swift

@@ -1,31 +1,42 @@
 /*
-  Two-dimensional array with a fixed number of rows and columns.
-  This is mostly handy for games that are played on a grid, such as chess.
-  Performance is always O(1).
-*/
+ Two-dimensional array with a fixed number of rows and columns.
+ This is mostly handy for games that are played on a grid, such as chess.
+ Performance is always O(1).
+ */
 public struct Array2D<T> {
-  public let columns: Int
-  public let rows: Int
-  fileprivate var array: [T]
-
-  public init(columns: Int, rows: Int, initialValue: T) {
-    self.columns = columns
-    self.rows = rows
-    array = .init(repeatElement(initialValue, count: rows*columns))
-  }
-
-  public subscript(column: Int, row: Int) -> T {
-    get {
-      return array[row*columns + column]
+    public let columns: Int
+    public let rows: Int
+    public var array: [T]
+    
+    public init(columns: Int, rows: Int, initialValue: T) {
+        self.columns = columns
+        self.rows = rows
+        array = [T](repeating: initialValue, count: rows*columns)
     }
-    set {
-      array[row*columns + column] = newValue
+    
+    public subscript(column: Int, row: Int) -> T {
+        get {
+            if isValidSubscript(column: column, row: row) {
+                return array[row*columns + column]
+            } else {
+                fatalError("Not a valid subscript")
+            }
+        }
+        set {
+            if isValidSubscript(column: column, row: row) {
+                array[row*columns + column] = newValue
+            } else {
+                fatalError("Not a valid subscript")
+            }
+        }
+    }
+    
+    private func isValidSubscript(column: Int, row: Int) -> Bool {
+        return column < columns && row < rows
     }
-  }
 }
 
 
-
 // initialization
 var matrix = Array2D(columns: 3, rows: 5, initialValue: 0)
 
@@ -51,13 +62,13 @@ print(matrix.array)
 
 // print out the 2D array with a reference around the grid
 for i in 0..<matrix.rows {
-  print("[", terminator: "")
-  for j in 0..<matrix.columns {
-    if j == matrix.columns - 1 {
-      print("\(matrix[j, i])", terminator: "")
-    } else {
-      print("\(matrix[j, i]) ", terminator: "")
+    print("[", terminator: "")
+    for j in 0..<matrix.columns {
+        if j == matrix.columns - 1 {
+            print("\(matrix[j, i])", terminator: "")
+        } else {
+            print("\(matrix[j, i]) ", terminator: "")
+        }
     }
-  }
-  print("]")
+    print("]")
 }