Data commit

Task/Modular-arithmetic/Swift/modular-arithmetic.swift

@@ -0,0 +1,60 @@
+precedencegroup ExponentiationGroup {
+  higherThan: MultiplicationPrecedence
+}
+
+infix operator ** : ExponentiationGroup
+
+protocol Ring {
+  associatedtype RingType: Numeric
+
+  var one: Self { get }
+
+  static func +(_ lhs: Self, _ rhs: Self) -> Self
+  static func *(_ lhs: Self, _ rhs: Self) -> Self
+  static func **(_ lhs: Self, _ rhs: Int) -> Self
+}
+
+extension Ring  {
+  static func **(_ lhs: Self, _ rhs: Int) -> Self {
+    var ret = lhs.one
+
+    for _ in stride(from: rhs, to: 0, by: -1) {
+      ret = ret * lhs
+    }
+
+    return ret
+  }
+}
+
+struct ModInt: Ring {
+  typealias RingType = Int
+
+  var value: Int
+  var modulo: Int
+
+  var one: ModInt { ModInt(1, modulo: modulo) }
+
+  init(_ value: Int, modulo: Int) {
+    self.value = value
+    self.modulo = modulo
+  }
+
+  static func +(lhs: ModInt, rhs: ModInt) -> ModInt {
+    precondition(lhs.modulo == rhs.modulo)
+
+    return ModInt((lhs.value + rhs.value) % lhs.modulo, modulo: lhs.modulo)
+  }
+
+  static func *(lhs: ModInt, rhs: ModInt) -> ModInt {
+    precondition(lhs.modulo == rhs.modulo)
+
+    return ModInt((lhs.value * rhs.value) % lhs.modulo, modulo: lhs.modulo)
+  }
+}
+
+func f<T: Ring>(_ x: T) -> T { (x ** 100) + x + x.one }
+
+let x = ModInt(10, modulo: 13)
+let y = f(x)
+
+print("x ^ 100 + x + 1 for x = ModInt(10, 13) is \(y)")