77 lines
1.7 KiB
Rust
77 lines
1.7 KiB
Rust
/*
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* File: recursion.rs
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* Created Time: 2023-09-02
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* Author: night-cruise (2586447362@qq.com)
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*/
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/* Recursion */
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fn recur(n: i32) -> i32 {
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// Termination condition
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if n == 1 {
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return 1;
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}
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// Recursive: recursive call
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let res = recur(n - 1);
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// Return: return result
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n + res
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}
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/* Simulate recursion with iteration */
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fn for_loop_recur(n: i32) -> i32 {
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// Use an explicit stack to simulate the system call stack
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let mut stack = Vec::new();
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let mut res = 0;
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// Recursive: recursive call
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for i in (1..=n).rev() {
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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.is_empty() {
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// Simulate "return" by "popping from the stack"
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res += stack.pop().unwrap();
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}
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// res = 1+2+3+...+n
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res
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}
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/* Tail recursion */
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fn tail_recur(n: i32, res: i32) -> i32 {
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// Termination condition
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if n == 0 {
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return res;
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}
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// Tail recursive call
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tail_recur(n - 1, res + n)
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}
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/* Fibonacci sequence: Recursion */
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fn fib(n: i32) -> i32 {
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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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}
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// Recursive call f(n) = f(n-1) + f(n-2)
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let res = fib(n - 1) + fib(n - 2);
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// Return result
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res
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}
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/* Driver Code */
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fn main() {
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let n = 5;
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let mut res;
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res = recur(n);
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println!("\nRecursive function sum result res = {res}");
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res = for_loop_recur(n);
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println!("\nSimulate recursion with iteration sum result res = {res}");
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res = tail_recur(n, 0);
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println!("\nTail recursive function sum result 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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}
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