43 lines
1.1 KiB
Swift
43 lines
1.1 KiB
Swift
/**
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* File: climbing_stairs_backtrack.swift
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* Created Time: 2023-07-15
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* Author: nuomi1 (nuomi1@qq.com)
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*/
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/* 回溯 */
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func backtrack(choices: [Int], state: Int, n: Int, res: inout [Int]) {
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// 当爬到第 n 阶时，方案数量加 1
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if state == n {
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res[0] += 1
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}
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// 遍历所有选择
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for choice in choices {
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// 剪枝：不允许越过第 n 阶
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if state + choice > n {
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continue
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}
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backtrack(choices: choices, state: state + choice, n: n, res: &res)
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}
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}
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/* 爬楼梯：回溯 */
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func climbingStairsBacktrack(n: Int) -> Int {
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let choices = [1, 2] // 可选择向上爬 1 阶或 2 阶
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let state = 0 // 从第 0 阶开始爬
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var res: [Int] = []
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res.append(0) // 使用 res[0] 记录方案数量
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backtrack(choices: choices, state: state, n: n, res: &res)
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return res[0]
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}
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@main
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enum ClimbingStairsBacktrack {
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/* Driver Code */
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static func main() {
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let n = 9
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let res = climbingStairsBacktrack(n: n)
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print("爬 \(n) 阶楼梯共有 \(res) 种方案")
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}
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}
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