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], and [3,2,1].

Solution 1

4ms 36.02%

public class Solution {
   public static List> permute(int[] nums) {
        List> lists = new ArrayList>();
        if(nums == null || nums.length == 0){
            return lists;
        }
        return permuteList(nums);
    }
    
    public static List> permuteList(int [] nums){
        if(nums.length == 1){
            List> result = new ArrayList>();
            result.add(Arrays.asList(nums[0]));
            return result;
        }
        List> lists = new ArrayList>();
        int c = nums[0];
        int [] newNum = new int [nums.length - 1];
        for(int i = 1; i < nums.length; i++){
            newNum[i - 1] = nums[i];
        }
        List> result = permuteList(newNum);
        for(List list : result){
            for(int i = 0; i <= list.size(); i++){
                List newList = insert(list, c, i);
                lists.add(newList);
            }
        }
        return lists;
    }
    public static List insert(List list, int c, int j){
    	List newList = new ArrayList();
        for(int i = 0; i < j; i++){
        	newList.add(list.get(i));
        }
        newList.add(c);
        for(int i = j; i < list.size(); i++){
        	newList.add(list.get(i));
        }
        return newList;
    }
    
    public static void main(String[] args) {
    	int [] nums = {1,2,3};
		permute(nums);
	}
    
}