【Leetcode】Permutations

题目链接：https://leetcode.com/problems/permutations/

题目：

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].

o see which companies asked this question

思路：

数组下标的三皇后问题，实质是全排列问题。唯一不同 都是，本题全排列的是数组的下标。只要做个对应转化就好了。

算法：

	List<List<Integer>> iLists = new ArrayList<List<Integer>>();

	public List<List<Integer>> permute(int[] nums) {
		this.n = nums.length;
		this.cl = new int[n];
		this.n2 = nums;
		dspPermute(0);
		return iLists;
	}

	int[] n2;
	int cl[] = null;
	int n = 0;

	void dspPermute(int cur) {
		if (cur == n) {
			List<Integer> list = new ArrayList<Integer>();
			for (int i = 0; i < cl.length; i++) {
				list.add(cl[i]);
			}
			iLists.add(list);
		} else {
			for (int i = 0; i < n; i++) { // 探索每一列
				cl[cur] = n2[i];// 选择n[i]为第cur个数
				boolean flag = true;
				for (int j = 0; j < cur; j++) {// cur前所有行 若无冲突
					if (cl[cur] == cl[j])
						flag = false;
				}
				if (flag == true) {
					dspPermute(cur + 1);
				}
			}
		}
	}