LeetCode | 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].

无重复数字的全排列就是每个数字轮流排第一，然后剩余的再全排列。

代码

import java.util.ArrayList;

public class Permutations {
	private ArrayList<ArrayList<Integer>> result;
	private int N;
	private ArrayList<Integer> list;

	public ArrayList<ArrayList<Integer>> permute(int[] num) {
		result = new ArrayList<ArrayList<Integer>>();
		N = num.length;
		list = new ArrayList<Integer>();
		for (int i = 0; i < N; ++i) {
			list.add(num[i]);
		}
		solve(0);
		return result;
	}

	private void solve(int k) {
		if (k >= N) {
			result.add(new ArrayList<Integer>(list));
			return;
		}
		for (int i = k; i < N; ++i) {
			swap(i, k);
			solve(k + 1);
			swap(i, k);
		}
	}

	private void swap(int i, int j) {
		int temp = list.get(i);
		list.set(i, list.get(j));
		list.set(j, temp);
	}
}

LeetCode | Permutations,布布扣,bubuko.com

LeetCode | Permutations

原文：http://blog.csdn.net/perfect8886/article/details/22312249