算法提高 快乐司机

import java.util.Arrays;
import java.util.Scanner;

/*
 * 典型的贪心算法的应用
 */
public class Main {
    static class Value implements Comparable<Value>{
        private int num;
        private double value;

        public Value(int num, double value) {
            super();
            this.num = num;
            this.value = value;
        }

        public int getNum() {
            return num;
        }

        public double getValue() {
            return value;
        }

        public int compareTo(Value o) {
            // TODO Auto-generated method stub
            double cmp = this.value - o.value;
            if ( cmp > 0.0){
                return 1;
            }else if ( cmp == 0.0){
                return 0;
            }else{
                return -1;
            }
        }
    }

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        Scanner in = new Scanner(System.in);
        int n = in.nextInt();
        int weight = in.nextInt();
        double sum = 0;
        Value[] Goods = new Value[n];
        int g;
        int p;
        for (int i = 0 ; i < n ; i++){
            g = in.nextInt();
            p = in.nextInt();
            Goods[i] = new Value(g, p*1.0/g);
        }
        Arrays.sort(Goods);
        for ( int i = n-1 ; i >= 0 ; i--){
            if ( weight > Goods[i].getNum()){
                sum += Goods[i].getValue()*Goods[i].getNum();
                weight -= Goods[i].getNum();
            }else{
                sum += weight*Goods[i].getValue();
                break;
            }
        }
        System.out.printf("%.1f",sum);
        in.close();
    }

}