Commendo War UVa-11729

“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

文章大意：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Bi分钟交待任务，然后他会立刻独立地、无间断地执行Ji分钟后完成任务。你需要选择交待任务的顺序，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，不能同时给两个部下交待任务，但部下们可以同时执行他们各自的任务。

分析：执行时间较长的任务应该先交待，于是想到用贪心算法：按J从大到小的顺序各个任务排序，然后依次交代。代码如下。

#include <iostream>#include <cstdio>#include <cstring>#include <algorithm>using namespace std;struct node{    int Ai,Bi;}s[1005];bool cmp(const node&a,const node &b){    return a.Bi>b.Bi;}int main(){    int n,k=1;    while(scanf("%d",&n)==1&&n)    {        memset(s,0,sizeof(node)*1005);//每次必须清除数组        for(int i=0;i<n;i++)        {            cin>>s[i].Ai>>s[i].Bi;        }        sort(s,s+n,cmp);//将部下按完成任务时间从大到小排序        int sum=0,ans=0;        for(int i=0;i<n;i++)        {            sum+=s[i].Ai;               //每个任务开始执行的时间            ans=max(ans,sum+s[i].Bi);   //更新任务执行完毕时的最晚时间        }        printf("Case %d: %d\n",k++,ans);    }    return 0;}