78 lines
1.8 KiB
Kotlin
78 lines
1.8 KiB
Kotlin
/**
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* File: recursion.kt
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* Created Time: 2024-01-25
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* Author: curtishd (1023632660@qq.com)
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*/
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package chapter_computational_complexity.recursion
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import java.util.*
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/* Recursion */
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fun recur(n: Int): Int {
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// Termination condition
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if (n == 1)
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return 1
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// Rec: Recursive call
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val res = recur(n - 1)
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// Return: Return result
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return n + res
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}
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/* Simulate recursion with iteration */
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fun forLoopRecur(n: Int): Int {
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// Use an explicit stack to simulate the system call stack
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val stack = Stack<Int>()
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var res = 0
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// Rec: Recursive call
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for (i in n downTo 0) {
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// Simulate "recursive" by "pushing onto the stack"
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stack.push(i)
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}
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// Return: Return result
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while (stack.isNotEmpty()) {
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// Simulate "return" by "popping from the stack"
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res += stack.pop()
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}
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// res = 1+2+3+...+n
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return res
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}
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/* Tail recursion */
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tailrec fun tailRecur(n: Int, res: Int): Int {
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// Add tailrec keyword to enable tail recursion optimization
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// Termination condition
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if (n == 0)
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return res
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// Tail recursive call
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return tailRecur(n - 1, res + n)
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}
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/* Fibonacci sequence: Recursion */
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fun fib(n: Int): Int {
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// Termination condition f(1) = 0, f(2) = 1
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if (n == 1 || n == 2)
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return n - 1
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// Recursive call f(n) = f(n-1) + f(n-2)
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val res = fib(n - 1) + fib(n - 2)
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// Return result f(n)
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return res
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}
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/* Driver Code */
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fun main() {
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val n = 5
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var res: Int
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res = recur(n)
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println("\nResult of recursive sum function res = $res")
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res = forLoopRecur(n)
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println("\nSum result using iteration to simulate recursion res = $res")
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res = tailRecur(n, 0)
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println("\nResult of tail-recursive sum function res = $res")
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res = fib(n)
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println("\nThe $n-th term of the Fibonacci sequence is $res")
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} |