[Leetcode] 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]
.
Solution:
1 public class Solution { 2 public List<List<Integer>> permuteUnique(int[] num) { 3 Arrays.sort(num); 4 List<List<Integer>> result=new ArrayList<List<Integer>>(); 5 List<Integer> al=new ArrayList<Integer>(); 6 boolean[] flag=new boolean[num.length]; 7 dfs(num,result,al,0,flag); 8 return result; 9 } 10 11 private void dfs(int[] num, List<List<Integer>> result, List<Integer> al, int level,boolean[] flag) { 12 // TODO Auto-generated method stub 13 if(level>num.length) 14 return; 15 if(level==num.length){ 16 result.add(new ArrayList<Integer>(al)); 17 return; 18 } 19 for(int i=0;i<num.length;++i){ 20 if(!flag[i]){ 21 flag[i]=true; 22 al.add(num[i]); 23 dfs(num, result, al, level+1, flag); 24 al.remove(al.size()-1); 25 flag[i]=false; 26 while((i+1<num.length)&&num[i]==num[i+1]) 27 ++i; 28 } 29 } 30 } 31 }