[LintCode] 带重复元素的排列

class Solution {
public:
/**
* @param nums: A list of integers.
* @return: A list of unique permutations.
*/
vector<vector<int> > permuteUnique(vector<int> &nums) {
// write your code here
sort(nums.begin(), nums.end());
vector<vector<int> > permutations;
if (nums.empty()) return permutations;
permutate(nums, 0, permutations);
return permutations;
}
private:
void permutate(vector<int> nums, int start, vector<vector<int> >& permutations) {
if (start == nums.size()) {
permutations.push_back(nums);
return;
}
for (int i = start; i < (int)nums.size(); i++) {
if (i == start || nums[i] != nums[start]) {
swap(nums[start], nums[i]);
permutate(nums, start + 1, permutations);
}
}
}
};

class Solution {
public:
/**
* @param nums: A list of integers.
* @return: A list of unique permutations.
*/
vector<vector<int> > permuteUnique(vector<int> &nums) {
// write your code here
vector<vector<int> > permutations;
if (nums.empty()) return permutations;
vector<int> copy(nums.begin(), nums.end());
nextPermutation(nums);
permutations.push_back(nums);
while (nums != copy) {
nextPermutation(nums);
permutations.push_back(nums);
}
return permutations;
}
private:
void nextPermutation(vector<int>& nums) {
int k = -1, n = nums.size();
for (int i = n - 2; i >= 0; i--) {
if (nums[i] < nums[i + 1]) {
k = i;
break;
}
}
if (k == -1) {
reverse(nums.begin(), nums.end());
return;
}
int l;
for (int i = n - 1; i > k; i--) {
if (nums[i] > nums[k]) {
l = i;
break;
}
}
swap(nums[l], nums[k]);
reverse(nums.begin() + k + 1, nums.end());
}
};