Data commit

Task/Bell-numbers/Swift/bell-numbers.swift

@@ -0,0 +1,43 @@
+public struct BellTriangle<T: BinaryInteger> {
+  @usableFromInline
+  var arr: [T]
+
+  @inlinable
+  public internal(set) subscript(row row: Int, col col: Int) -> T {
+    get { arr[row * (row - 1) / 2 + col] }
+    set { arr[row * (row - 1) / 2 + col] = newValue }
+  }
+
+  @inlinable
+  public init(n: Int) {
+    arr = Array(repeating: 0, count: n * (n + 1) / 2)
+
+    self[row: 1, col: 0] = 1
+
+    for i in 2...n {
+      self[row: i, col: 0] = self[row: i - 1, col: i - 2]
+
+      for j in 1..<i {
+        self[row: i, col: j] = self[row: i, col: j - 1] + self[row: i - 1, col: j - 1]
+      }
+    }
+  }
+}
+
+let tri = BellTriangle<Int>(n: 15)
+
+print("First 15 Bell numbers:")
+
+for i in 1...15 {
+  print("\(i): \(tri[row: i, col: 0])")
+}
+
+for i in 1...10 {
+  print(tri[row: i, col: 0], terminator: "")
+
+  for j in 1..<i {
+    print(", \(tri[row: i, col: j])", terminator: "")
+  }
+
+  print()
+}