全排列

/**
 * 46.全排列<br/>
 * https://leetcode-cn.com/problems/permutations/<br>
 * @author wuwang
 *
 */
public class p46 {
	List<List<Integer>> result = new LinkedList<>();
	int[] nums;
	int length;

	public List<List<Integer>> permute(int[] nums) {
		this.nums = nums;
		length = nums.length;
		dfs(0);
		return result;
	}

	// 1 2 3
	// 1 3 2

	public void swap(int[] arr, int x, int y) {
		int temp = arr[x];
		arr[x] = arr[y];
		arr[y] = temp;
	}


	public void dfs(int begin) {
		if (begin == nums.length) {
			result.add(toArray(nums));
		} else {
			for (int i = begin; i < nums.length; ++i) {
				swap(nums, i, begin);// 这里的交换非常精妙
				dfs(begin + 1);
				swap(nums, i, begin);// 还原
			}
		}
	}

	public List<Integer> toArray(int... args) {
		LinkedList<Integer> arr = new LinkedList<Integer>();
		for (int i : args) {
			arr.add(i);
		}
		return arr;
	}
}