LeetCode-46 Permutations(全排列)

LeetCode-46 Permutations(全排列)

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 List<List<Integer>> permute(int[] num) {
		List<List<Integer>> llist = new ArrayList<List<Integer>>();
		quanpailie(num, 0, num.length, llist);
		return llist;
    }
	public static void swap(int[] num,int a,int b) {
		int temp = num[a];
		num[a] = num;
		num[b] = temp;
	}
	public static void quanpailie(int[] num,int l,int n,List<List<Integer>> llist){
		if (l >= n) {
			List<Integer> list = new ArrayList<Integer>();
			for (int i = 0; i < num.length; i++) {
				list.add(num[i]);
			}
			llist.add(list);
		}
		for (int i = l; i < n; i++) {
			swap(num, i, l);
			quanpailie(num, l+1, n,llist);
			swap(num, i, l);
		}
	}
}

Runtime: [b]264 ms



分析：很重要也很基本的全排列算法。



.