java实现排列组合(通俗易懂)

个人感觉这篇文章(原文地址见文章尾)写的排列组合问题,非常的好,而且是一步一步引出排列组合问题,我也是看了这篇文章,一步一步按照这个思路来,最后会了自己的一套排列组合

也因此在算法竞赛中,两次用到了,成功解决了问题.

第一个问题:

　　首先,先让我们来看第一个问题, 有1,2,3,4这4个数字.可以重复的在里面选4次,问能得到多少种结果.easy

　　1　　1　　1　　1

　　1　　1　　1　　2

　　1　　1　　1　　3　　

　　1　　1　　1　　4

　　1　　1　　2　　1

　　1　　1　　2　　2

　　.......

　　4　　4　　4　　3

　　4　　4　　4　　4

　　代码实现其实也很简单,大家可以看下代码,理解一下,再自己敲一下,应该可以很快敲出来

import java.util.Stack;

public class Main {
	
	public static Stack<Integer> stack = new Stack<Integer>();
	public static void main(String[] args) {
		int shu[] = {1,2,3,4};
		f(shu,4,0);
	}
	/**
	 * 
	 * @param shu	待选择的数组
	 * @param targ	要选择多少个次
	 * @param cur	当前选择的是第几次
	 */
	private static void f(int[] shu, int targ, int cur) {
		// TODO Auto-generated method stub
		if(cur == targ) {
			System.out.println(stack);
			return;
		}
		
		for(int i=0;i<shu.length;i++) {
			stack.add(shu[i]);
			f(shu, targ, cur+1);
			stack.pop();
			
		}
	}

}

　　输出:

[1, 1, 1, 1]
[1, 1, 1, 2]
[1, 1, 1, 3]
[1, 1, 1, 4]
[1, 1, 2, 1]
[1, 1, 2, 2]
[1, 1, 2, 3]
[1, 1, 2, 4]
[1, 1, 3, 1]
[1, 1, 3, 2]
[1, 1, 3, 3]
[1, 1, 3, 4]
[1, 1, 4, 1]
[1, 1, 4, 2]
[1, 1, 4, 3]
[1, 1, 4, 4]
[1, 2, 1, 1]
[1, 2, 1, 2]
[1, 2, 1, 3]
[1, 2, 1, 4]
[1, 2, 2, 1]
[1, 2, 2, 2]
[1, 2, 2, 3]
[1, 2, 2, 4]
[1, 2, 3, 1]
[1, 2, 3, 2]
[1, 2, 3, 3]
[1, 2, 3, 4]
[1, 2, 4, 1]
[1, 2, 4, 2]
[1, 2, 4, 3]
[1, 2, 4, 4]
[1, 3, 1, 1]
[1, 3, 1, 2]
[1, 3, 1, 3]
[1, 3, 1, 4]
[1, 3, 2, 1]
[1, 3, 2, 2]
[1, 3, 2, 3]
[1, 3, 2, 4]
[1, 3, 3, 1]
[1, 3, 3, 2]
[1, 3, 3, 3]
[1, 3, 3, 4]
[1, 3, 4, 1]
[1, 3, 4, 2]
[1, 3, 4, 3]
[1, 3, 4, 4]
[1, 4, 1, 1]
[1, 4, 1, 2]
[1, 4, 1, 3]
[1, 4, 1, 4]
[1, 4, 2, 1]
[1, 4, 2, 2]
[1, 4, 2, 3]
[1, 4, 2, 4]
[1, 4, 3, 1]
[1, 4, 3, 2]
[1, 4, 3, 3]
[1, 4, 3, 4]
[1, 4, 4, 1]
[1, 4, 4, 2]
[1, 4, 4, 3]
[1, 4, 4, 4]
[2, 1, 1, 1]
[2, 1, 1, 2]
[2, 1, 1, 3]
[2, 1, 1, 4]
[2, 1, 2, 1]
[2, 1, 2, 2]
[2, 1, 2, 3]
[2, 1, 2, 4]
[2, 1, 3, 1]
[2, 1, 3, 2]
[2, 1, 3, 3]
[2, 1, 3, 4]
[2, 1, 4, 1]
[2, 1, 4, 2]
[2, 1, 4, 3]
[2, 1, 4, 4]
[2, 2, 1, 1]
[2, 2, 1, 2]
[2, 2, 1, 3]
[2, 2, 1, 4]
[2, 2, 2, 1]
[2, 2, 2, 2]
[2, 2, 2, 3]
[2, 2, 2, 4]
[2, 2, 3, 1]
[2, 2, 3, 2]
[2, 2, 3, 3]
[2, 2, 3, 4]
[2, 2, 4, 1]
[2, 2, 4, 2]
[2, 2, 4, 3]
[2, 2, 4, 4]
[2, 3, 1, 1]
[2, 3, 1, 2]
[2, 3, 1, 3]
[2, 3, 1, 4]
[2, 3, 2, 1]
[2, 3, 2, 2]
[2, 3, 2, 3]
[2, 3, 2, 4]
[2, 3, 3, 1]
[2, 3, 3, 2]
[2, 3, 3, 3]
[2, 3, 3, 4]
[2, 3, 4, 1]
[2, 3, 4, 2]
[2, 3, 4, 3]
[2, 3, 4, 4]
[2, 4, 1, 1]
[2, 4, 1, 2]
[2, 4, 1, 3]
[2, 4, 1, 4]
[2, 4, 2, 1]
[2, 4, 2, 2]
[2, 4, 2, 3]
[2, 4, 2, 4]
[2, 4, 3, 1]
[2, 4, 3, 2]
[2, 4, 3, 3]
[2, 4, 3, 4]
[2, 4, 4, 1]
[2, 4, 4, 2]
[2, 4, 4, 3]
[2, 4, 4, 4]
[3, 1, 1, 1]
[3, 1, 1, 2]
[3, 1, 1, 3]
[3, 1, 1, 4]
[3, 1, 2, 1]
[3, 1, 2, 2]
[3, 1, 2, 3]
[3, 1, 2, 4]
[3, 1, 3, 1]
[3, 1, 3, 2]
[3, 1, 3, 3]
[3, 1, 3, 4]
[3, 1, 4, 1]
[3, 1, 4, 2]
[3, 1, 4, 3]
[3, 1, 4, 4]
[3, 2, 1, 1]
[3, 2, 1, 2]
[3, 2, 1, 3]
[3, 2, 1, 4]
[3, 2, 2, 1]
[3, 2, 2, 2]
[3, 2, 2, 3]
[3, 2, 2, 4]
[3, 2, 3, 1]
[3, 2, 3, 2]
[3, 2, 3, 3]
[3, 2, 3, 4]
[3, 2, 4, 1]
[3, 2, 4, 2]
[3, 2, 4, 3]
[3, 2, 4, 4]
[3, 3, 1, 1]
[3, 3, 1, 2]
[3, 3, 1, 3]
[3, 3, 1, 4]
[3, 3, 2, 1]
[3, 3, 2, 2]
[3, 3, 2, 3]
[3, 3, 2, 4]
[3, 3, 3, 1]
[3, 3, 3, 2]
[3, 3, 3, 3]
[3, 3, 3, 4]
[3, 3, 4, 1]
[3, 3, 4, 2]
[3, 3, 4, 3]
[3, 3, 4, 4]
[3, 4, 1, 1]
[3, 4, 1, 2]
[3, 4, 1, 3]
[3, 4, 1, 4]
[3, 4, 2, 1]
[3, 4, 2, 2]
[3, 4, 2, 3]
[3, 4, 2, 4]
[3, 4, 3, 1]
[3, 4, 3, 2]
[3, 4, 3, 3]
[3, 4, 3, 4]
[3, 4, 4, 1]
[3, 4, 4, 2]
[3, 4, 4, 3]
[3, 4, 4, 4]
[4, 1, 1, 1]
[4, 1, 1, 2]
[4, 1, 1, 3]
[4, 1, 1, 4]
[4, 1, 2, 1]
[4, 1, 2, 2]
[4, 1, 2, 3]
[4, 1, 2, 4]
[4, 1, 3, 1]
[4, 1, 3, 2]
[4, 1, 3, 3]
[4, 1, 3, 4]
[4, 1, 4, 1]
[4, 1, 4, 2]
[4, 1, 4, 3]
[4, 1, 4, 4]
[4, 2, 1, 1]
[4, 2, 1, 2]
[4, 2, 1, 3]
[4, 2, 1, 4]
[4, 2, 2, 1]
[4, 2, 2, 2]
[4, 2, 2, 3]
[4, 2, 2, 4]
[4, 2, 3, 1]
[4, 2, 3, 2]
[4, 2, 3, 3]
[4, 2, 3, 4]
[4, 2, 4, 1]
[4, 2, 4, 2]
[4, 2, 4, 3]
[4, 2, 4, 4]
[4, 3, 1, 1]
[4, 3, 1, 2]
[4, 3, 1, 3]
[4, 3, 1, 4]
[4, 3, 2, 1]
[4, 3, 2, 2]
[4, 3, 2, 3]
[4, 3, 2, 4]
[4, 3, 3, 1]
[4, 3, 3, 2]
[4, 3, 3, 3]
[4, 3, 3, 4]
[4, 3, 4, 1]
[4, 3, 4, 2]
[4, 3, 4, 3]
[4, 3, 4, 4]
[4, 4, 1, 1]
[4, 4, 1, 2]
[4, 4, 1, 3]
[4, 4, 1, 4]
[4, 4, 2, 1]
[4, 4, 2, 2]
[4, 4, 2, 3]
[4, 4, 2, 4]
[4, 4, 3, 1]
[4, 4, 3, 2]
[4, 4, 3, 3]
[4, 4, 3, 4]
[4, 4, 4, 1]
[4, 4, 4, 2]
[4, 4, 4, 3]
[4, 4, 4, 4]

第二个问题:

　　同理, 问题来了,这时候有点排列组合的意思了,1,2,3,4排列要的到的是

　有没有发现要的到排列的情况,这里stack里的元素是1,2,3,4都不能重复

那么我在入栈的时候加个判断,如果比如1,已经在stack里面了,就不加进去,就不会得到 1 　　1　　1　　1　...的情况了,就得到了排列

import java.util.Stack;

public class Main {
	
	public static Stack<Integer> stack = new Stack<Integer>();
	public static void main(String[] args) {
		int shu[] = {1,2,3,4};
		f(shu,4,0);
	}
	/**
	 * 
	 * @param shu	待选择的数组
	 * @param targ	要选择多少个次
	 * @param cur	当前选择的是第几次
	 */
	private static void f(int[] shu, int targ, int cur) {
		// TODO Auto-generated method stub
		if(cur == targ) {
			System.out.println(stack);
			return;
		}
		
		for(int i=0;i<shu.length;i++) {
			if(!stack.contains(shu[i])) {
				stack.add(shu[i]);
				f(shu, targ, cur+1);
				stack.pop();
			}
			
		}
	}

}

　　输出:

[1, 2, 3, 4]
[1, 2, 4, 3]
[1, 3, 2, 4]
[1, 3, 4, 2]
[1, 4, 2, 3]
[1, 4, 3, 2]
[2, 1, 3, 4]
[2, 1, 4, 3]
[2, 3, 1, 4]
[2, 3, 4, 1]
[2, 4, 1, 3]
[2, 4, 3, 1]
[3, 1, 2, 4]
[3, 1, 4, 2]
[3, 2, 1, 4]
[3, 2, 4, 1]
[3, 4, 1, 2]
[3, 4, 2, 1]
[4, 1, 2, 3]
[4, 1, 3, 2]
[4, 2, 1, 3]
[4, 2, 3, 1]
[4, 3, 1, 2]
[4, 3, 2, 1]

这就是想要的排列结果了..

第三个问题:

明天待续....

原文地址: https://blog.csdn.net/Ring_k/article/details/79575533

java实现排列组合(通俗易懂)

猜你喜欢