47.Permutations 1&2

標籤：

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));    }}

 

47.Permutations 1&2