UVa 11729 - Commando War(贪心)

“Waiting for orders we held in the wood, word from the front never came

By evening the sound of the gunfire was miles away

Ah softly we moved through the shadows, slip away through the trees

Crossing their lines in the mists in the fields on our hands and our knees

And all that I ever, was able to see

The fire in the air, glowing red, silhouetting the smoke on the breeze”

There is a war and it doesn’t look very promising for your country. Now it’s time to act. You

have a commando squad at your disposal and planning an ambush on an important enemy camp

located nearby. You have N soldiers in your squad. In your master-plan, every single soldier has a

unique responsibility and you don’t want any of your soldier to know the plan for other soldiers so that

everyone can focus on his task only. In order to enforce this, you brief every individual soldier about

his tasks separately and just before sending him to the battlefield. You know that every single soldier

needs a certain amount of time to execute his job. You also know very clearly how much time you

need to brief every single soldier. Being anxious to finish the total operation as soon as possible, you

need to find an order of briefing your soldiers that will minimize the time necessary for all the soldiers

to complete their tasks. You may assume that, no soldier has a plan that depends on the tasks of his

fellows. In other words, once a soldier begins a task, he can finish it without the necessity of pausing

in between.

Input

There will be multiple test cases in the input file. Every test case starts with an integer N (1 ≤

N ≤ 1000), denoting the number of soldiers. Each of the following N lines describe a soldier with two

integers B (1 ≤ B ≤ 10000) & J (1 ≤ J ≤ 10000). B seconds are needed to brief the soldier while

completing his job needs J seconds. The end of input will be denoted by a case with N = 0. This case

should not be processed.

Output

For each test case, print a line in the format, ‘Case X: Y ’, where X is the case number & Y is the

total number of seconds counted from the start of your first briefing till the completion of all jobs.

Sample Input

3

2 5

3 2

2 1

3

3 3

4 4

5 5

0

Sample Output

Case 1: 8

Case 2: 15

题意：

你有n个部下，每个部下需要完成一项任务。第i个部下需要你花B(i)分钟交代任务，

然后他就会立刻独立的、无间断的执行J(i)分钟后完成任务。

你需要选择交代任务的顺序，使得所有任务尽早执行完毕(即最后一个执行完的任务应尽早结束)。

注意：不能同时给2个或以上的部下交代任务，但部下们可以同时执行他们各自的任务。

输入第一行为n，n为部下的个数。

接下来的n行为B和J。

当n为0时，输入结束。

分析：

执行时间较长的任务需要先交代，

于是，我们可以想到这样一个贪心算法：

按照J从小到大的顺序给各个任务排序，然后依次交代。

package cn.hncu.UVa;

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

/**
 *
 * @author 陈浩翔
 *
 * 2016-4-25
 */
public class P11729 {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int k=0;
        while(sc.hasNext()){
            k++;
            int n =sc.nextInt();
            if(n==0){
                break;
            }
            Bj bj[] = new Bj[n];
            for(int i=0;i<n;i++){
                bj[i]=new Bj();
                bj[i].b = sc.nextInt();
                bj[i].j = sc.nextInt();
            }
            sort(bj);
            int s=0;
            int ans =0;
            for(int i=0;i<n;i++){
                s = s+bj[i].b;//当前任务的开始执行时间，也就是吩咐完后的时间
                ans = Math.max(ans, s+bj[i].j);//更新用户任务执行完毕时的最晚时间
            }
            System.out.println("Case "+k+": "+ans);
        }
    }

    private static void sort(Bj[] bj) {
        Arrays.sort(bj, new Comparator<Bj>() {
            @Override
            public int compare(Bj o1, Bj o2) {
                if(o1.j<o2.j){
                    return 1;
                }
                return -1;
            }
        });
    }
}

class Bj{
    public int b;
    public int j;
}