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krahets
2024-05-06 14:40:36 +08:00
parent 7e7eb6047a
commit 5c7d2c7f17
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en/docs/chapter_backtracking/permutations_problem.md
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@@ -89,9 +89,38 @@ After understanding the above information, we can "fill in the blanks" in the fr
=== "C++"
```cpp title="permutations_i.cpp"
[class]{}-[func]{backtrack}
/* Backtracking algorithm: Permutation I */
void backtrack(vector<int> &state, const vector<int> &choices, vector<bool> &selected, vector<vector<int>> &res) {
// When the state length equals the number of elements, record the solution
if (state.size() == choices.size()) {
res.push_back(state);
return;
}
// Traverse all choices
for (int i = 0; i < choices.size(); i++) {
int choice = choices[i];
// Pruning: do not allow repeated selection of elements
if (!selected[i]) {
// Attempt: make a choice, update the state
selected[i] = true;
state.push_back(choice);
// Proceed to the next round of selection
backtrack(state, choices, selected, res);
// Retract: undo the choice, restore to the previous state
selected[i] = false;
state.pop_back();
}
}
}
[class]{}-[func]{permutationsI}
/* Permutation I */
vector<vector<int>> permutationsI(vector<int> nums) {
vector<int> state;
vector<bool> selected(nums.size(), false);
vector<vector<int>> res;
backtrack(state, nums, selected, res);
return res;
}
```
=== "Java"
@@ -285,9 +314,40 @@ Based on the code from the previous problem, we consider initiating a hash set `
=== "C++"
```cpp title="permutations_ii.cpp"
[class]{}-[func]{backtrack}
/* Backtracking algorithm: Permutation II */
void backtrack(vector<int> &state, const vector<int> &choices, vector<bool> &selected, vector<vector<int>> &res) {
// When the state length equals the number of elements, record the solution
if (state.size() == choices.size()) {
res.push_back(state);
return;
}
// Traverse all choices
unordered_set<int> duplicated;
for (int i = 0; i < choices.size(); i++) {
int choice = choices[i];
// Pruning: do not allow repeated selection of elements and do not allow repeated selection of equal elements
if (!selected[i] && duplicated.find(choice) == duplicated.end()) {
// Attempt: make a choice, update the state
duplicated.emplace(choice); // Record selected element values
selected[i] = true;
state.push_back(choice);
// Proceed to the next round of selection
backtrack(state, choices, selected, res);
// Retract: undo the choice, restore to the previous state
selected[i] = false;
state.pop_back();
}
}
}
[class]{}-[func]{permutationsII}
/* Permutation II */
vector<vector<int>> permutationsII(vector<int> nums) {
vector<int> state;
vector<bool> selected(nums.size(), false);
vector<vector<int>> res;
backtrack(state, nums, selected, res);
return res;
}
```
=== "Java"