79 lines
2.1 KiB
C#
79 lines
2.1 KiB
C#
/**
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* File: recursion.cs
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* Created Time: 2023-08-28
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* Author: hpstory (hpstory1024@163.com)
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*/
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namespace hello_algo.chapter_computational_complexity;
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public class recursion {
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/* Recursion */
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int Recur(int n) {
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// Termination condition
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if (n == 1)
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return 1;
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// Recursive: recursive call
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int 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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int ForLoopRecur(int n) {
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// Use an explicit stack to simulate the system call stack
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Stack<int> stack = new();
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int res = 0;
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// Recursive: recursive call
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for (int i = n; i > 0; i--) {
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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.Count > 0) {
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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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int TailRecur(int n, int res) {
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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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int Fib(int n) {
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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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int 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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[Test]
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public void Test() {
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int n = 5;
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int res;
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res = Recur(n);
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Console.WriteLine("\nSum result of the recursive function res =" + res);
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res = ForLoopRecur(n);
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Console.WriteLine("\nSum result using iteration to simulate recursion res =" + res);
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res = TailRecur(n, 0);
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Console.WriteLine("\nSum result of the tail-recursive function res =" + res);
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res = Fib(n);
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Console.WriteLine("\nThe " + n + "th number in the Fibonacci sequence is" + res);
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}
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}
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