leetcode 46 problem permutation in java code example

Example: leetcode 46 problem permutation in java

public ArrayList<ArrayList<Integer>> permute(int[] num) {
	ArrayList<ArrayList<Integer>> result = new ArrayList<ArrayList<Integer>>();
 
	//start from an empty list
	result.add(new ArrayList<Integer>());
 
	for (int i = 0; i < num.length; i++) {
		//list of list in current iteration of the array num
		ArrayList<ArrayList<Integer>> current = new ArrayList<ArrayList<Integer>>();
 
		for (ArrayList<Integer> l : result) {
			// # of locations to insert is largest index + 1
			for (int j = 0; j < l.size()+1; j++) {
				// + add num[i] to different locations
				l.add(j, num[i]);
 
				ArrayList<Integer> temp = new ArrayList<Integer>(l);
				current.add(temp);
 
				//System.out.println(temp);
 
				// - remove num[i] add
				l.remove(j);
			}
		}
 
		result = new ArrayList<ArrayList<Integer>>(current);
	}
 
	return result;
}