80 lines
1.9 KiB
Swift
80 lines
1.9 KiB
Swift
/**
|
|
* File: recursion.swift
|
|
* Created Time: 2023-09-02
|
|
* Author: nuomi1 (nuomi1@qq.com)
|
|
*/
|
|
|
|
/* Recursion */
|
|
func recur(n: Int) -> Int {
|
|
// Termination condition
|
|
if n == 1 {
|
|
return 1
|
|
}
|
|
// Recursive: recursive call
|
|
let res = recur(n: n - 1)
|
|
// Return: return result
|
|
return n + res
|
|
}
|
|
|
|
/* Simulate recursion with iteration */
|
|
func forLoopRecur(n: Int) -> Int {
|
|
// Use an explicit stack to simulate the system call stack
|
|
var stack: [Int] = []
|
|
var res = 0
|
|
// Recursive: recursive call
|
|
for i in (1 ... n).reversed() {
|
|
// Simulate "recursive" by "pushing onto the stack"
|
|
stack.append(i)
|
|
}
|
|
// Return: return result
|
|
while !stack.isEmpty {
|
|
// Simulate "return" by "popping from the stack"
|
|
res += stack.removeLast()
|
|
}
|
|
// res = 1+2+3+...+n
|
|
return res
|
|
}
|
|
|
|
/* Tail recursion */
|
|
func tailRecur(n: Int, res: Int) -> Int {
|
|
// Termination condition
|
|
if n == 0 {
|
|
return res
|
|
}
|
|
// Tail recursive call
|
|
return tailRecur(n: n - 1, res: res + n)
|
|
}
|
|
|
|
/* Fibonacci sequence: Recursion */
|
|
func fib(n: Int) -> Int {
|
|
// Termination condition f(1) = 0, f(2) = 1
|
|
if n == 1 || n == 2 {
|
|
return n - 1
|
|
}
|
|
// Recursive call f(n) = f(n-1) + f(n-2)
|
|
let res = fib(n: n - 1) + fib(n: n - 2)
|
|
// Return result f(n)
|
|
return res
|
|
}
|
|
|
|
@main
|
|
enum Recursion {
|
|
/* Driver Code */
|
|
static func main() {
|
|
let n = 5
|
|
var res = 0
|
|
|
|
res = recursion.recur(n: n)
|
|
print("\nResult of recursive sum function res = \(res)")
|
|
|
|
res = recursion.forLoopRecur(n: n)
|
|
print("\nSum result of iterative simulation of recursion res = \(res)")
|
|
|
|
res = recursion.tailRecur(n: n, res: 0)
|
|
print("\nSum result of tail recursion function res = \(res)")
|
|
|
|
res = recursion.fib(n: n)
|
|
print("\nThe \(n)th term of Fibonacci sequence is \(res)")
|
|
}
|
|
}
|