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53 lines
1.4 KiB
53 lines
1.4 KiB
/**
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* File: permutations_i.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_backtracking.permutations_i
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/* 回溯算法：全排列 I */
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fun backtrack(
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state: MutableList<Int>,
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choices: IntArray,
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selected: BooleanArray,
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res: MutableList<MutableList<Int>?>
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) {
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// 当状态长度等于元素数量时，记录解
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if (state.size == choices.size) {
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res.add(state.toMutableList())
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return
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}
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// 遍历所有选择
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for (i in choices.indices) {
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val choice = choices[i]
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// 剪枝：不允许重复选择元素
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if (!selected[i]) {
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// 尝试：做出选择，更新状态
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selected[i] = true
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state.add(choice)
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// 进行下一轮选择
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backtrack(state, choices, selected, res)
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// 回退：撤销选择，恢复到之前的状态
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selected[i] = false
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state.removeAt(state.size - 1)
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}
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}
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}
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/* 全排列 I */
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fun permutationsI(nums: IntArray): MutableList<MutableList<Int>?> {
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val res = mutableListOf<MutableList<Int>?>()
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backtrack(mutableListOf(), nums, BooleanArray(nums.size), res)
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return res
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}
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/* Driver Code */
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fun main() {
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val nums = intArrayOf(1, 2, 3)
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val res = permutationsI(nums)
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println("输入数组 nums = ${nums.contentToString()}")
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println("所有排列 res = $res")
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} |