47.Permutations 1&2

1.Given a collection of numbers, return all possible permutations.

For example,
[1,2,3] have the following permutations:
[1,2,3], [1,3,2], [2,1,3], [2,3,1], [3,1,2], and [3,2,1].

2.

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:DFS

       1                      2                           3

  12    13              21     23                  32  31

123      132         213     231             321    312

 

package leetcode2;

import java.util.*;

public class Permutations {
     public static ArrayList<ArrayList<Integer>> permute(int[] num) {
         ArrayList<ArrayList<Integer>> res=new ArrayList<ArrayList<Integer>>();
         ArrayList<Integer>  mem =new  ArrayList<Integer>();
         int deep=0;
         int length=num.length;
         boolean visit[]=new boolean[length];
         dfs(res,mem,deep,num,visit,length);
         return res;
        }
     
    public static void dfs(ArrayList<ArrayList<Integer>> res,
            ArrayList<Integer> mem, int deep, int[] num,boolean[] visit,int l) {
        
        // TODO Auto-generated method stub
        if(deep==l){
            if(!res.contains(new ArrayList<Integer>(mem))){
            res.add(new ArrayList<Integer>(mem));
            }
            return;
        }
        if(deep<l){
            for(int i=0;i<l;i++){
                if(i>0 && num[i-1] == num[i] && !visit[i-1])
                 continue;
                if(!visit[i]){
                mem.add(num[i]);
                visit[i]=true;
                dfs(res,mem,deep+1,num,visit,l);
                if(mem.size()>0){
                mem.remove(mem.size()-1);
                visit[i]=false;
                }
                }
            }
        }
        if(deep>num.length)
            return;
    }

    public static void main(String[] args) {
        // TODO Auto-generated method stub
     int[] a={1,2,3};
     System.out.print(permute(a));
    }

}