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57 lines
1.7 KiB
57 lines
1.7 KiB
6 months ago
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/**
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* File: permutations_ii.cpp
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* Created Time: 2023-04-24
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* Author: krahets (krahets@163.com)
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*/
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#include "../utils/common.hpp"
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/* Backtracking algorithm: Permutation II */
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void backtrack(vector<int> &state, const vector<int> &choices, vector<bool> &selected, vector<vector<int>> &res) {
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// When the state length equals the number of elements, record the solution
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if (state.size() == choices.size()) {
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res.push_back(state);
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return;
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}
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// Traverse all choices
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unordered_set<int> duplicated;
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for (int i = 0; i < choices.size(); i++) {
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int choice = choices[i];
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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.find(choice) == duplicated.end()) {
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// Attempt: make a choice, update the state
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duplicated.emplace(choice); // Record selected element values
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selected[i] = true;
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state.push_back(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.pop_back();
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}
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}
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}
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/* Permutation II */
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vector<vector<int>> permutationsII(vector<int> nums) {
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vector<int> state;
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vector<bool> selected(nums.size(), false);
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vector<vector<int>> res;
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backtrack(state, nums, selected, res);
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return res;
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}
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/* Driver Code */
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int main() {
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vector<int> nums = {1, 1, 2};
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vector<vector<int>> res = permutationsII(nums);
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cout << "Input array nums = ";
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printVector(nums);
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cout << "All permutations res = ";
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printVectorMatrix(res);
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return 0;
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}
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