leetcode 047 Permutations II

Given a collection of numbers that might contain duplicates, return all possible unique permutations.

For example,

[1,1,2]

 have the following unique permutations:

[1,1,2]

, 

[1,2,1]

,
and 

[2,1,1]

.

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class Solution {
public:
bool generateNext(vector<int> &nums) {
int len = nums.size(), i = 0, j = 0;

for(i = len-2; i >= 0; i--) {
if(nums[i] < nums[i+1]) break;
}

if(i < 0) return false;

for(j = len-1; j > i; j--) {
if(nums[j] > nums[i]) break;
}

int temp = nums[j];
nums[j] = nums[i];
nums[i] = temp;

for(int l = i+1, r = len-1; l <= r; l++, r--) {
temp = nums[r];
nums[r] = nums[l];
nums[l] = temp;
}

return true;
}

vector<vector<int> > permuteUnique(vector<int>& nums) {
sort(nums.begin(), nums.end());
vector<vector<int> > ans;
ans.push_back(nums);
while(generateNext(nums)) {
ans.push_back(nums);
}

return ans;
}
};