s0047
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include/s0047_permutations_ii.hpp
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include/s0047_permutations_ii.hpp
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#ifndef S0047_PERMUTATIONS_II_HPP
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#define S0047_PERMUTATIONS_II_HPP
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#include <algorithm>
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#include <vector>
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using namespace std;
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class S0047 {
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public:
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vector<vector<int>> permuteUnique(vector<int>& nums);
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};
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#endif
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# 排列问题
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## [46. 全排列](https://leetcode.cn/problems/permutations/)
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## [47. 全排列 II](https://leetcode.cn/problems/permutations-ii/)
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和 s0046 相比就加了去重。有两种去重思路,一个是用哈希表记录每一层的使用情况。另一种是排序 + 判断,后者性能更好所以优先选择后者。
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哈希表法:
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```cpp
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#include "s0047_permutations_ii.hpp"
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void permuteUniqueDFS(vector<int> &path, vector<vector<int>> &result,
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vector<bool> &used, vector<int> &nums) {
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int len = nums.size();
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// 终止条件
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if (path.size() == len) {
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result.push_back(path);
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return;
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}
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// 创建一个哈希表用来记录当前层中使用过的元素
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unordered_map<int, bool> map;
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// 开始迭代
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for (int i{0}; i < len; ++i) {
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// 如果当前元素在树枝或树层使用过,则跳过
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if (used[i] || map.count(nums[i]) == 1) continue;
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// 否则处理当前节点
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map[nums[i]] = true;
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path.push_back(nums[i]);
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used[i] = true;
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permuteUniqueDFS(path, result, used, nums);
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used[i] = false;
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path.pop_back();
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}
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}
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vector<vector<int>> S0047::permuteUnique(vector<int> &nums) {
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vector<int> path{};
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vector<vector<int>> result{};
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vector<bool> used(nums.size(), false);
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permuteUniqueDFS(path, result, used, nums);
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return result;
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}
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```
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排序 + 判断:
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```cpp
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void permuteUniqueDFS(vector<int> &path, vector<vector<int>> &result,
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vector<bool> &used, vector<int> &nums, int startIndex) {
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int len = nums.size();
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// 终止条件
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if (path.size() == len) {
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result.push_back(path);
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return;
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}
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// 开始迭代
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for (int i{0}; i < len; ++i) {
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// 如果当前元素在树层使用过,则跳过
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if (used[i] || (i > 0 && nums[i] == nums[i - 1] && used[i - 1] == false))
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continue;
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// 否则处理当前节点
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path.push_back(nums[i]);
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used[i] = true;
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permuteUniqueDFS(path, result, used, nums, i + 1);
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used[i] = false;
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path.pop_back();
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}
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}
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vector<vector<int>> S0047::permuteUnique(vector<int> &nums) {
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vector<int> path{};
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vector<vector<int>> result{};
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vector<bool> used(nums.size(), false);
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sort(nums.begin(), nums.end());
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permuteUniqueDFS(path, result, used, nums, 0);
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return result;
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}
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```
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33
src/s0047_permutations_ii.cpp
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src/s0047_permutations_ii.cpp
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#include "s0047_permutations_ii.hpp"
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void permuteUniqueDFS(vector<int> &path, vector<vector<int>> &result,
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vector<bool> &used, vector<int> &nums, int startIndex) {
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int len = nums.size();
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// 终止条件
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if (path.size() == len) {
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result.push_back(path);
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return;
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}
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// 开始迭代
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for (int i{0}; i < len; ++i) {
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// 如果当前元素在树层使用过,则跳过
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if (used[i] || (i > 0 && nums[i] == nums[i - 1] && used[i - 1] == false))
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continue;
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// 否则处理当前节点
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path.push_back(nums[i]);
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used[i] = true;
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permuteUniqueDFS(path, result, used, nums, i + 1);
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used[i] = false;
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path.pop_back();
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}
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}
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vector<vector<int>> S0047::permuteUnique(vector<int> &nums) {
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vector<int> path{};
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vector<vector<int>> result{};
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vector<bool> used(nums.size(), false);
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sort(nums.begin(), nums.end());
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permuteUniqueDFS(path, result, used, nums, 0);
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return result;
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}
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