53 lines
1.7 KiB
Swift
53 lines
1.7 KiB
Swift
/**
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* File: permutations_ii.swift
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* Created Time: 2023-04-30
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* Author: nuomi1 (nuomi1@qq.com)
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*/
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/* Backtracking algorithm: Permutation II */
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func backtrack(state: inout [Int], choices: [Int], selected: inout [Bool], res: inout [[Int]]) {
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// When the state length equals the number of elements, record the solution
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if state.count == choices.count {
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res.append(state)
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return
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}
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// Traverse all choices
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var duplicated: Set<Int> = []
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for (i, choice) in choices.enumerated() {
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// Pruning: do not allow repeated selection of elements and do not allow repeated selection of equal elements
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if !selected[i], !duplicated.contains(choice) {
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// Attempt: make a choice, update the state
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duplicated.insert(choice) // Record selected element values
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selected[i] = true
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state.append(choice)
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// Proceed to the next round of selection
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backtrack(state: &state, choices: choices, selected: &selected, res: &res)
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// Retract: undo the choice, restore to the previous state
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selected[i] = false
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state.removeLast()
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}
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}
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}
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/* Permutation II */
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func permutationsII(nums: [Int]) -> [[Int]] {
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var state: [Int] = []
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var selected = Array(repeating: false, count: nums.count)
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var res: [[Int]] = []
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backtrack(state: &state, choices: nums, selected: &selected, res: &res)
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return res
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}
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@main
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enum PermutationsII {
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/* Driver Code */
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static func main() {
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let nums = [1, 2, 3]
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let res = permutationsII(nums: nums)
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print("Input array nums = \(nums)")
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print("All permutations res = \(res)")
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}
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}
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