52 lines
1.3 KiB
Dart
52 lines
1.3 KiB
Dart
/**
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* File: permutations_i.dart
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* Created Time: 2023-08-10
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* Author: liuyuxin (gvenusleo@gmail.com)
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*/
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/* Backtracking algorithm: Permutation I */
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void backtrack(
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List<int> state,
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List<int> choices,
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List<bool> selected,
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List<List<int>> res,
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) {
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// When the state length equals the number of elements, record the solution
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if (state.length == choices.length) {
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res.add(List.from(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.removeLast();
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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(List<int> nums) {
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List<List<int>> res = [];
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backtrack([], nums, List.filled(nums.length, false), res);
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return res;
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}
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/* Driver Code */
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void main() {
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List<int> nums = [1, 2, 3];
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List<List<int>> res = permutationsI(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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