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42 lines
1.1 KiB
42 lines
1.1 KiB
/*
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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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/* 回溯 */
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fn backtrack(choices: &[i32], state: i32, n: i32, res: &mut [i32]) {
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// 當爬到第 n 階時，方案數量加 1
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if state == n {
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res[0] = res[0] + 1;
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}
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// 走訪所有選擇
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for &choice in choices {
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// 剪枝：不允許越過第 n 階
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if state + choice > n {
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continue;
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}
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// 嘗試：做出選擇，更新狀態
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backtrack(choices, state + choice, n, res);
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// 回退
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}
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}
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/* 爬樓梯：回溯 */
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fn climbing_stairs_backtrack(n: usize) -> i32 {
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let choices = vec![1, 2]; // 可選擇向上爬 1 階或 2 階
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let state = 0; // 從第 0 階開始爬
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let mut res = Vec::new();
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res.push(0); // 使用 res[0] 記錄方案數量
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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!("爬 {n} 階樓梯共有 {res} 種方案");
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}
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