leetcode Permutations

题目链接

思路：
递归回溯。典型应用

public class Solution {    int n;    List<List<Integer>>  result;    List<Integer> temp;    boolean  isUsed[];    int[]nums;    public List<List<Integer>> permute(int[] nums) {        n=nums.length;        isUsed=new boolean[n];        temp=new LinkedList<Integer>();        result=new LinkedList<List<Integer>>();        this.nums=nums;        help(0);        return result;    }    public void help(int step)    {        if(step==n)        {            result.add(new LinkedList<Integer>(temp));            return;        }        for(int i= 0;i<n;i++)        {            if(!isUsed[i])            {                isUsed[i]=true;                temp.add(nums[i]);                help(step+1);                isUsed[i]=false;                temp.remove(temp.size()-1);            }        }    }}