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44 lines
1.1 KiB
44 lines
1.1 KiB
/**
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* File: climbing_stairs_backtrack.kt
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* Created Time: 2024-01-25
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* Author: curtishd (1023632660@qq.com)
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*/
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package chapter_dynamic_programming
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/* 回溯 */
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fun backtrack(
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choices: List<Int>,
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state: Int,
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n: Int,
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res: MutableList<Int>
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) {
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// 当爬到第 n 阶时，方案数量加 1
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if (state == n) res[0] = res[0] + 1
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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) continue
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// 尝试：做出选择，更新状态
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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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/* 爬楼梯：回溯 */
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fun climbingStairsBacktrack(n: Int): Int {
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val choices = mutableListOf(1, 2) // 可选择向上爬 1 阶或 2 阶
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val state = 0 // 从第 0 阶开始爬
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val res = ArrayList<Int>()
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res.add(0) // 使用 res[0] 记录方案数量
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backtrack(choices, state, n, res)
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return res[0]
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}
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/* Driver Code */
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fun main() {
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val n = 9
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val res = climbingStairsBacktrack(n)
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println("爬 $n 阶楼梯共有 $res 种方案")
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} |