活动安排问题

活动安排问题

贪心算法

一问题分析

二代码实现

java
package greedySelctor;

import java.io.BufferedWriter;
import java.io.FileWriter;
import java.io.IOException;
import java.util.Arrays;
import java.util.Comparator;

public class bin
{

public static void main(String[] args) throws IOException
{

// int []s= {0,1,3,0,5,3,5,6,8,8,2,12};
// int []f= {0,4,5,6,7,8,9,10,11,12,13,14};
int []s= {0,1,2,3,4,5,6};
int []f= {0,10,9,8,7,11,20};
element []ele=new element[s.length-1] ;
for(int i=1; i<s.length; i++)
{
ele[i-1] =new element(s[i], f[i], i);
}
greedySelctor myGreedySelctor=new greedySelctor(ele);
}

}
class greedySelctor
{
element []ele;
int count=0; //被安排活动的个数
public greedySelctor(element []ele) throws IOException
{
this.ele=ele;
GreedySelctor();
display();
}
public void GreedySelctor()
{
Arrays.sort(ele, new Comparator(){
//传入的时候由用户自己选
@Override
public int compare(element o1, element o2) {
// TODO Auto-generated method stub
int finsh1 = o1.f;
int finsh2 = o2.f;
if (finsh1>finsh2)
{
return 1;
}
else
{
if (finsh1<finsh2)
{
return -1;
}else
{
return 0;
}

		    }
			
		}
	});
	ele[0].x=1;  //第一个活动一定会被选上
	int f=ele[0].f;
	count++;
	for(int i=1; i<ele.length; i++)
	{
		if(f<=ele[i].s)  //安排
		{
		   ele[i].x=1;
		   f=ele[i].f;
		}
		else
		{
			ele[i].x=0;
		}
	}
}
public void display() throws IOException
{
	BufferedWriter fout=new BufferedWriter(new FileWriter("out.txt"));
	for(int i=0; i<ele.length; i++)
	{
		fout.write("ele["+i+"]:");
		fout.newLine();
		fout.write("i:\t"+ele[i].i);
		fout.newLine();
		fout.write("s:\t"+ele[i].s);
		fout.newLine();
		fout.write("f:\t"+ele[i].f);
		fout.newLine();
		fout.write("x:\t"+ele[i].x);
		fout.newLine();
	    fout.write("+++++++++++++++++++");
	    fout.newLine();
	}
	fout.flush();
}

}
class element //活动类
{
int s; //开始时间
int f; //结束
int x; //是否被选中
int i; //编号
public element(int s,int f,int i)
{
this.s=s;
this.f=f;
this.i=i;
}
}

三 运行结果
ele[0]:
i: 1
s: 1
f: 4
x: 1
+++++++++++++++++++
ele[1]:
i: 2
s: 3
f: 5
x: 0
+++++++++++++++++++
ele[2]:
i: 3
s: 0
f: 6
x: 0
+++++++++++++++++++
ele[3]:
i: 4
s: 5
f: 7
x: 1
+++++++++++++++++++
ele[4]:
i: 5
s: 3
f: 8
x: 0
+++++++++++++++++++
ele[5]:
i: 6
s: 5
f: 9
x: 0
+++++++++++++++++++
ele[6]:
i: 7
s: 6
f: 10
x: 0
+++++++++++++++++++
ele[7]:
i: 8
s: 8
f: 11
x: 1
+++++++++++++++++++
ele[8]:
i: 9
s: 8
f: 12
x: 0
+++++++++++++++++++
ele[9]:
i: 10
s: 2
f: 13
x: 0
+++++++++++++++++++
ele[10]:
i: 11
s: 12
f: 14
x: 1
+++++++++++++++++++

四 总结收获

1. 贪心算法的关键在于问题具有贪心性质

2. 学习到了对象数组排序的方法
   Arrays.sort(ele, new Comparator(){
   //传入的时候由用户自己选
   @Override
   public int compare(element o1, element o2) {
   // TODO Auto-generated method stub
   int finsh1 = o1.f;
   int finsh2 = o2.f;
   if (finsh1>finsh2)
   {
   return 1;
   }
   else
   {
   if (finsh1<finsh2)
   {
   return -1;
   }else
   {
   return 0;
   }

   	    }
   		
   	}
   });
   
   具体解释见链接(https://blog.csdn.net/qq_37937537/article/details/80445731)
   

   五 不足
   代码写的不够熟练