Data commit

Task/100-prisoners/Swift/100-prisoners.swift

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+import Foundation
+
+struct PrisonersGame {
+  let strategy: Strategy
+  let numPrisoners: Int
+  let drawers: [Int]
+
+  init(numPrisoners: Int, strategy: Strategy) {
+    self.numPrisoners = numPrisoners
+    self.strategy = strategy
+    self.drawers = (1...numPrisoners).shuffled()
+  }
+
+  @discardableResult
+  func play() -> Bool {
+    for num in 1...numPrisoners {
+      guard findNumber(num) else {
+        return false
+      }
+    }
+
+    return true
+  }
+
+  private func findNumber(_ num: Int) -> Bool {
+    var tries = 0
+    var nextDrawer = num - 1
+
+    while tries < 50 {
+      tries += 1
+
+      switch strategy {
+      case .random where drawers.randomElement()! == num:
+        return true
+      case .optimum where drawers[nextDrawer] == num:
+        return true
+      case .optimum:
+        nextDrawer = drawers[nextDrawer] - 1
+      case _:
+        continue
+      }
+    }
+
+    return false
+  }
+
+  enum Strategy {
+    case random, optimum
+  }
+}
+
+let numGames = 100_000
+let lock = DispatchSemaphore(value: 1)
+var done = 0
+
+print("Running \(numGames) games for each strategy")
+
+DispatchQueue.concurrentPerform(iterations: 2) {i in
+  let strat = i == 0 ? PrisonersGame.Strategy.random : .optimum
+  var numPardoned = 0
+
+  for _ in 0..<numGames {
+    let game = PrisonersGame(numPrisoners: 100, strategy: strat)
+
+    if game.play() {
+      numPardoned += 1
+    }
+  }
+
+  print("Probability of pardon with \(strat) strategy: \(Double(numPardoned) / Double(numGames))")
+
+  lock.wait()
+  done += 1
+  lock.signal()
+
+  if done == 2 {
+    exit(0)
+  }
+}
+
+dispatchMain()