四个实例超详细讲解Java 贪心和枚举的特点与使用

for ( int i= 0 ;i< 1 <<n;i++){  //i为1到2^n的状态压缩值   2^n

     int p=i;          //先将i取出

     int sum= 0 ;        //用一个变量维护取出的数之和

     for (j= 0 ;j<n;j++){   //转为二进制进行操作

         sum+=p% 2 *a[j];    //这句话是求取出来的数之和。p%2为对应二进制位

                          //这里也可以进行其他操作，不一一举例。

         p/= 2 ;            //求下一个二进制位

         }

      //这里可以添加想要的操作。

    }

import java.io.*;

import java.util.*;

public class Main{

     public static class Orange{

             int acid;

             int sweet;

             public Orange( int acid, int sweet){

                 this .acid = acid;

                 this .sweet = sweet;

             }

             public Orange(){}

         }

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

         BufferedReader br = new BufferedReader( new InputStreamReader(System.in));

         String[] tmp = br.readLine().split( " " );

         int n = Integer.parseInt(tmp[ 0 ]);

         int k = Integer.parseInt((tmp[ 1 ]));

         String[] ai = br.readLine().split( " " );

         String[] bi = br.readLine().split( " " );

         //定义一个优先队列，并根据指定的比较器对其元素进行排序。

         PriorityQueue<Orange> queue = new PriorityQueue<>((Orange o1, Orange o2)->{

             //匿名内部类以lambda的形式定义排序规则

             if (o1.sweet == o2.sweet){

                 return o1.acid - o2.acid;

             } else {

                 return o2.sweet - o1.sweet;

             }

         });

         for ( int i = 0 ; i < n; i++){

             Orange orange = new Orange();

             orange.acid = Integer.parseInt(ai[i]);

             orange.sweet = Integer.parseInt(bi[i]);

             queue.add(orange);

         }

         long totalAcid = 0 ;

         long totalSweet = 0 ;

         for ( int i = 0 ; i < k; i++){

             Orange o = queue.poll();

             totalAcid += o.acid;

             totalSweet += o.sweet;

         }

         System.out.println(totalAcid + " " + totalSweet);

     }

}

import java.io.*;

import java.util.*;

class Point{

     double x;

     double y;

}

public class Main{

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

         BufferedReader br = new BufferedReader( new InputStreamReader(System.in));

         int n = Integer.parseInt(br.readLine());

         Point[] points = new Point[n];

         for ( int i= 0 ;i<n;i++){

             String[] strings = br.readLine().split( " " );

             Point point = new Point();

             point.x = Integer.parseInt(strings[ 0 ]);

             point.y = Integer.parseInt(strings[ 1 ]);

             points[i] = point;

         }

         double min = Double.MAX_VALUE; //定义最大值，寻找较小值

         //双层遍历枚举

         for ( int i= 0 ;i<n- 1 ;i++) {

             for ( int j=i+ 1 ;j<n;j++) {

                 double temp = Math.sqrt(points[i].x*points[i].x + points[i].y*points[i].y)

                         + Math.sqrt(points[j].x*points[j].x + points[j].y*points[j].y)

                         + Math.sqrt((points[i].x-points[j].x)*(points[i].x-points[j].x) + (points[i].y-points[j].y)*(points[i].y-points[j].y));

                 min = Math.min(min, temp);

             }

         }

         System.out.println(String.format( "%.6f" , min));

     }

}

import java.util.*;

import java.io.*;

public class Main{

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

         BufferedReader br = new BufferedReader( new InputStreamReader(System.in));

         Long x= Long.parseLong(br.readLine());

         //循环0到2^18来展现所有的可能性

         for ( int i= 0 ;i< 1 << 19 ;i++){

             long p=i,s1= 0 ,s2= 0 ,temp=x;

             //将p拟化为2进制，通过j来寻尾。寻一次p就对应的二进制数就少一位。

             for ( int j= 0 ;j< 19 ;j++){

                 if (p% 2 == 1 )s1+=temp% 10 ;

                 else s2+=temp% 10 ;

                 p/= 2 ;

                 temp/= 10 ;

             }

             if (s1==s2){

                 System.out.println( "Yes" );

                 System.exit( 0 );

             }

         }

         System.out.println( "No" );

     }

}

for ( int i= 0 ;i< 1 << 19 ;i++) 

//修改成

  for ( int i= 0 ;i< 19 ;i++) p1[i]=p1[i- 1 ]* 3 ;

  for ( int i= 0 ;i<p1[i];i++){}

import java.util.*;

import java.io.*;

public class Main{

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

         BufferedReader br = new BufferedReader( new InputStreamReader(System.in));

         String s1 = br.readLine();

         String s2 = br.readLine();

         ArrayList<Integer> a1 = new ArrayList<>();

         ArrayList<Integer> a2 = new ArrayList<>();

         for ( int i = 0 ; i < 60 * 24 ; i++){

             int hour = i/ 60 , minute = i% 60 ;

             if ((hour/ 10 == s1.charAt( 0 )- '0' || s1.charAt( 0 ) == '?' ) &&

                (hour% 10 == s1.charAt( 1 )- '0' || s1.charAt( 1 ) == '?' ) &&

                (minute/ 10 == s1.charAt( 3 )- '0' || s1.charAt( 3 ) == '?' ) &&

                (minute% 10 == s1.charAt( 4 )- '0' || s1.charAt( 4 ) == '?' )) a1.add(i);

             if ((hour/ 10 == s2.charAt( 0 )- '0' || s2.charAt( 0 ) == '?' ) &&

                (hour% 10 == s2.charAt( 1 )- '0' || s2.charAt( 1 ) == '?' ) &&

                (minute/ 10 == s2.charAt( 3 )- '0' || s2.charAt( 3 ) == '?' ) &&

                (minute% 10 == s2.charAt( 4 )- '0' || s2.charAt( 4 ) == '?' ))a2.add(i);

         }

         int min= Integer.MAX_VALUE, max = Integer.MIN_VALUE;

         for ( int i = 0 ; i<a1.size();i++){

             for ( int j = 0 ; j<a2.size();j++){

                 if (a1.get(i)<a2.get(j)){

                     min = Math.min(min,a2.get(j)-a1.get(i));

                     max = Math.max(max,a2.get(j)-a1.get(i));

                 }

             }

         }

         System.out.print(min + " " + max);

     }

}