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45 lines
1.1 KiB
45 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: MutableList<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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// 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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// 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) continue
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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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fun climbingStairsBacktrack(n: Int): Int {
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val choices = mutableListOf(1, 2) // 可選擇向上爬 1 階或 2 階
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val state = 0 // 從第 0 階開始爬
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val res = mutableListOf<Int>()
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res.add(0) // 使用 res[0] 記錄方案數量
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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 階樓梯共有 $res 種方案")
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} |