[LeetCode] Permutations II

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Total Accepted: 8649 Total Submissions: 35072

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].

public class Solution {    public ArrayList<ArrayList<Integer>> permuteUnique(int[] num) {        ArrayList<ArrayList<Integer>>   list = new ArrayList<ArrayList<Integer>>();                dfs(num, list, 0);                return list;    }        // swap each element into num[index]    public void dfs(int[] num, ArrayList<ArrayList<Integer>> list, int index) {        if(index == num.length) {            ArrayList<Integer> path = new ArrayList<Integer>();            for (int i = 0; i < num.length; i++) path.add(num[i]);            list.add(path);            return;        }                for (int i = index; i < num.length; i++) {            boolean isDup = false;                        for (int k = index; k < i ; k++ ) {                if (num[k] == num[i]) isDup = true;            }                        if (!isDup){                swap(num, index, i);                dfs(num, list, index + 1);                swap(num, index, i);            }        }    }        public void swap(int[] num, int a, int b) {        int tmp = num[a];        num[a]  = num[b];        num[b]  = tmp;    }}

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