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Sainnhe Park 2023-02-03 17:01:25 +08:00
parent cea6c387a3
commit a40cbdf78e
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#ifndef S0047_PERMUTATIONS_II_HPP
#define S0047_PERMUTATIONS_II_HPP
#include <algorithm>
#include <vector>
using namespace std;
class S0047 {
public:
vector<vector<int>> permuteUnique(vector<int>& nums);
};
#endif

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# 排列问题
## [46. 全排列](https://leetcode.cn/problems/permutations/)
## [47. 全排列 II](https://leetcode.cn/problems/permutations-ii/)
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。
哈希表法:
```cpp
#include "s0047_permutations_ii.hpp"
void permuteUniqueDFS(vector<int> &path, vector<vector<int>> &result,
vector<bool> &used, vector<int> &nums) {
int len = nums.size();
// 终止条件
if (path.size() == len) {
result.push_back(path);
return;
}
// 创建一个哈希表用来记录当前层中使用过的元素
unordered_map<int, bool> map;
// 开始迭代
for (int i{0}; i < len; ++i) {
// 如果当前元素在树枝或树层使用过,则跳过
if (used[i] || map.count(nums[i]) == 1) continue;
// 否则处理当前节点
map[nums[i]] = true;
path.push_back(nums[i]);
used[i] = true;
permuteUniqueDFS(path, result, used, nums);
used[i] = false;
path.pop_back();
}
}
vector<vector<int>> S0047::permuteUnique(vector<int> &nums) {
vector<int> path{};
vector<vector<int>> result{};
vector<bool> used(nums.size(), false);
permuteUniqueDFS(path, result, used, nums);
return result;
}
```
排序 + 判断:
```cpp
void permuteUniqueDFS(vector<int> &path, vector<vector<int>> &result,
vector<bool> &used, vector<int> &nums, int startIndex) {
int len = nums.size();
// 终止条件
if (path.size() == len) {
result.push_back(path);
return;
}
// 开始迭代
for (int i{0}; i < len; ++i) {
// 如果当前元素在树层使用过,则跳过
if (used[i] || (i > 0 && nums[i] == nums[i - 1] && used[i - 1] == false))
continue;
// 否则处理当前节点
path.push_back(nums[i]);
used[i] = true;
permuteUniqueDFS(path, result, used, nums, i + 1);
used[i] = false;
path.pop_back();
}
}
vector<vector<int>> S0047::permuteUnique(vector<int> &nums) {
vector<int> path{};
vector<vector<int>> result{};
vector<bool> used(nums.size(), false);
sort(nums.begin(), nums.end());
permuteUniqueDFS(path, result, used, nums, 0);
return result;
}
```

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#include "s0047_permutations_ii.hpp"
void permuteUniqueDFS(vector<int> &path, vector<vector<int>> &result,
vector<bool> &used, vector<int> &nums, int startIndex) {
int len = nums.size();
// 终止条件
if (path.size() == len) {
result.push_back(path);
return;
}
// 开始迭代
for (int i{0}; i < len; ++i) {
// 如果当前元素在树层使用过,则跳过
if (used[i] || (i > 0 && nums[i] == nums[i - 1] && used[i - 1] == false))
continue;
// 否则处理当前节点
path.push_back(nums[i]);
used[i] = true;
permuteUniqueDFS(path, result, used, nums, i + 1);
used[i] = false;
path.pop_back();
}
}
vector<vector<int>> S0047::permuteUnique(vector<int> &nums) {
vector<int> path{};
vector<vector<int>> result{};
vector<bool> used(nums.size(), false);
sort(nums.begin(), nums.end());
permuteUniqueDFS(path, result, used, nums, 0);
return result;
}