46. Permutations

Given a collection of distinct 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], [3,2,1] ]

public class Solution {
    private List> ans = new ArrayList>();
    
    public List> permute(int[] nums) {
        // Arrays.sort(nums);
      //  List result = new ArrayList();
        if(nums.length<=0||nums == null)
           return ans;
        dfs(0,nums);
        return ans;
    }
    
    void dfs(int start,int[] nums)
    {
        if(start == nums.length)
        {
            List temp = new ArrayList();
            for(int i=0;i