47. 全排列 II

package leetcode;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

public class demo_47 {
    public List<List<Integer>> permuteUnique(int[] nums) {
        Arrays.sort(nums);
        int visited[]=new int[nums.length];
        List<List<Integer>> list=new ArrayList<List<Integer>>();
        backtrack(list, nums, new ArrayList<Integer>(), visited);
        System.out.println(list);
        return list;
    }
    public void backtrack(List<List<Integer>> list,int nums[],List<Integer> alist,int[] visited) {
        if(alist.size()==nums.length) {
            list.add(new ArrayList<Integer>(alist));
        }
        else {
            for(int i=0;i<nums.length;i++) {
                //降低重复，visited[i-1]==0指只要重复的数字第一次被使用，后面出现的都是第一次的重复，所以舍去
                if(i!=0&&nums[i]==nums[i-1]&&visited[i-1]==0) {continue;}
                if(visited[i]==1) {continue;}
                else {
                    alist.add(nums[i]);
                    visited[i]=1;
                    backtrack(list, nums, alist, visited);
                    alist.remove(alist.size()-1);
                    visited[i]=0;
                }
            }
        }
    }
    public static void main(String[] args) {
        // TODO Auto-generated method stub
        int nums[]= {1,1,1,2};
        demo_47 d47=new demo_47();
        d47.permuteUnique(nums);
    }

}