54 lines
1.7 KiB
C#
54 lines
1.7 KiB
C#
/**
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* File: permutations_i.cs
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* Created Time: 2023-04-24
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* Author: hpstory (hpstory1024@163.com)
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*/
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namespace hello_algo.chapter_backtracking;
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public class permutations_i {
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/* Backtracking algorithm: Permutation I */
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void Backtrack(List<int> state, int[] choices, bool[] selected, List<List<int>> res) {
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// When the state length equals the number of elements, record the solution
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if (state.Count == choices.Length) {
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res.Add(new List<int>(state));
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return;
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}
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// Traverse all choices
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for (int i = 0; i < choices.Length; i++) {
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int choice = choices[i];
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// Pruning: do not allow repeated selection of elements
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if (!selected[i]) {
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// Attempt: make a choice, update the state
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selected[i] = true;
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state.Add(choice);
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// Proceed to the next round of selection
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Backtrack(state, choices, selected, 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.RemoveAt(state.Count - 1);
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}
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}
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}
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/* Permutation I */
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List<List<int>> PermutationsI(int[] nums) {
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List<List<int>> res = [];
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Backtrack([], nums, new bool[nums.Length], res);
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return res;
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}
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[Test]
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public void Test() {
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int[] nums = [1, 2, 3];
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List<List<int>> res = PermutationsI(nums);
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Console.WriteLine("Input array nums = " + string.Join(", ", nums));
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Console.WriteLine("All permutations res =");
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foreach (List<int> permutation in res) {
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PrintUtil.PrintList(permutation);
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}
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}
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}
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