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 {    public List
     
      
       > permute(int[] nums) {        if(nums==null || nums.length==0){
   return null;}        List
       
        
         > resList=new ArrayList
         
          
           >(); List
           
             item=new ArrayList
            
             (); boolean[] isVisited=new boolean[nums.length]; backTracking(nums, item, resList, isVisited); return resList; } public void backTracking(int[] nums, List
             
               item, List
              
               
                > resList, boolean[] isVisited){ if(item.size()==nums.length){ resList.add(new ArrayList
                
                 (item)); return; } for(int i=0; i