Permutations @LeetCode

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].

	package leetcode.combinations;
	import java.util.ArrayList;
	import java.util.Arrays;
	/**
	* Problem: How to make it as Permutation according to combination?
	* -- don't use position as start marker. Help only has three parameters.
	*
	* Every time we can get other element from whole int[],start from 0, so i=0, just need to remove duplicate
	*
	* if list.size() == num.length, we add a result and return, Actually, remove return; will not have influence on final result.
	* the program will slow because it will enter following loop until go out.
	* (Every time it contains, and continue because of full of different elements stored already)
	*
	* In addition, we remove Arrays.sort(num) because permutation don't care non-descending order.
	*
	* @author jeffwan
	* @date Feb 10, 2014
	*/
	public class Permutations {
	public ArrayList<ArrayList<Integer>> permute(int[] num) {
	ArrayList<ArrayList<Integer>> result = new ArrayList<ArrayList<Integer>>();
	ArrayList<Integer> list = new ArrayList<Integer>();
	permuteHelper(result, list, num);
	return result;
	}
	private void permuteHelper(ArrayList<ArrayList<Integer>> result,
	ArrayList<Integer> list, int[] num) {
	if (list.size() == num.length) {
	result.add(new ArrayList<Integer>(list));
	return;
	}
	for (int i = 0; i < num.length; i++) {
	if (list.contains(num[i])) {
	continue;
	}
	list.add(num[i]);
	permuteHelper(result, list, num);
	list.remove(list.size() - 1);
	}
	}
	}

view raw Permutations.java hosted with ❤ by GitHub