/**
* Given a collection of numbers that might contain duplicates, return all possible unique
* permutations.
*
* <p>For example, [1,1,2] have the following unique permutations: [1,1,2], [1,2,1], and [2,1,1].
*
* @param nums
* @return
*/
public static List<List<Integer>> permuteUnique(int[] nums) {
List<List<Integer>> result = new ArrayList<List<Integer>>();
if (nums.length == 0) {
return result;
}
Arrays.sort(nums);
int count = 0;
while (true) {
// try to find next number by dictionary order
NextPermutation.nextPermutation(nums);
List<Integer> list = new ArrayList<Integer>();
for (int i = 0; i < nums.length; i++) {
list.add(nums[i]);
}
if (result.contains(list)) {
// break when same number appears.
break;
} else {
result.add(list);
}
}
return result;
}
private static boolean step(MutableArray<Integer> list) {
return NextPermutation.step(list, new DefaultComparator<Integer>());
}