78 lines
1.8 KiB
C
78 lines
1.8 KiB
C
/**
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* File: recursion.c
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* Created Time: 2023-09-09
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* Author: Gonglja (glj0@outlook.com)
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*/
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#include "../utils/common.h"
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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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int stack[1000]; // Use a large array to simulate a stack
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int top = -1; // Stack top index
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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[1 + top++] = i;
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}
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// Return: return result
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while (top >= 0) {
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// Simulate "return" by "popping from the stack"
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res += stack[top--];
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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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int main() {
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int n = 5;
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int res;
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res = recur(n);
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printf("\nResult of recursive sum function res = %d\n", res);
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res = forLoopRecur(n);
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printf("\nSum result using iteration to simulate recursion res = %d\n", res);
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res = tailRecur(n, 0);
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printf("\nResult of tail-recursive sum function res = %d\n", res);
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res = fib(n);
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printf("\nThe %d-th term of the Fibonacci sequence is %d\n", n, res);
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return 0;
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}
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