42 lines
1.2 KiB
Rust
42 lines
1.2 KiB
Rust
/*
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* File: climbing_stairs_backtrack.rs
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* Created Time: 2023-07-09
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* Author: codingonion (coderonion@gmail.com)
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*/
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/* Backtracking */
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fn backtrack(choices: &[i32], state: i32, n: i32, res: &mut [i32]) {
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// When climbing to the nth step, add 1 to the number of solutions
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if state == n {
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res[0] = res[0] + 1;
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}
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// Traverse all choices
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for &choice in choices {
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// Pruning: do not allow climbing beyond the nth step
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if state + choice > n {
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continue;
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}
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// Attempt: make a choice, update the state
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backtrack(choices, state + choice, n, res);
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// Retract
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}
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}
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/* Climbing stairs: Backtracking */
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fn climbing_stairs_backtrack(n: usize) -> i32 {
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let choices = vec![1, 2]; // Can choose to climb up 1 step or 2 steps
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let state = 0; // Start climbing from the 0th step
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let mut res = Vec::new();
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res.push(0); // Use res[0] to record the number of solutions
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backtrack(&choices, state, n as i32, &mut res);
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res[0]
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}
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/* Driver Code */
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pub fn main() {
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let n: usize = 9;
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let res = climbing_stairs_backtrack(n);
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println!("Climb {n} steps, there are {res} solutions in total");
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}
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