Permutations

Given a collection of 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].

public class Solution {
    public ArrayList<ArrayList<Integer>> res;
	public ArrayList<Integer> list;
	public ArrayList<ArrayList<Integer>> permute(int[] num) {
		// Start typing your Java solution below
		// DO NOT write main() function
		res = new ArrayList<ArrayList<Integer>>();
		list = new ArrayList<Integer>();
		perm(num, 0);
		return res;
	}
	public void perm(int[] num, int cur){
		if(cur == num.length){
			for(int i = 0; i < num.length; i++)
				list.add(num[i]);
			res.add(list);
			list = new ArrayList<Integer>();
		}
		for(int i = cur; i < num.length; i++){
			int temp = num[i];
			num[i] = num[cur];
			num[cur] = temp;
			perm(num, cur + 1);
			temp = num[i];
			num[i] = num[cur];
			num[cur] = temp;
		}
	}
}