P2920 [USACO08NOV]時間管理Time Management

題目描述

Ever the maturing businessman, Farmer John realizes that he must manage his time effectively. He has N jobs conveniently numbered 1..N (1 <= N <= 1,000) to accomplish (like milking the cows, cleaning the barn, mending the fences, and so on).

To manage his time effectively, he has created a list of the jobs that must be finished. Job i requires a certain amount of time T_i (1 <= T_i <= 1,000) to complete and furthermore must be finished by time S_i (1 <= S_i <= 1,000,000). Farmer John starts his day at time t=0 and can only work on one job at a time until it is finished.

Even a maturing businessman likes to sleep late; help Farmer John determine the latest he can start working and still finish all the jobs on time.

作為一名忙碌的商人，約翰知道必須高效地安排他的時間.他有N工作要 做，比如給奶牛擠奶，清洗牛棚，修理柵欄之類的.

為了高效，列出了所有工作的清單.第i分工作需要T_i單位的時間來完成，而 且必須在S_i或之前完成.現在是0時刻.約翰做一份工作必須直到做完才能停 止.

所有的商人都喜歡睡懶覺.請幫約翰計算他最遲什麽時候開始工作，可以讓所有工作按時完 成.

輸入輸出格式

• Line 1: A single integer: N

• Lines 2..N+1: Line i+1 contains two space-separated integers: T_i and S_i

• Line 1: The latest time Farmer John can start working or -1 if Farmer John cannot finish all the jobs on time.

輸入輸出樣例

4 
3 5 
8 14 
5 20 
1 16 

2 

說明

Farmer John has 4 jobs to do, which take 3, 8, 5, and 1 units of time, respectively, and must be completed by time 5, 14, 20, and 16, respectively.

Farmer John must start the first job at time 2. Then he can do the second, fourth, and third jobs in that order to finish on time.

#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>
using namespace std;
struct nond{
    int v,f;
}work[1005];
int n,ans;
bool cmp(nond x,nond y){
    return x.f>y.f;
}
int main(){
    scanf("%d",&n);
    for(int i=1;i<=n;i++)
        scanf("%d%d",&work[i].v,&work[i].f);
    sort(work+1,work+1+n,cmp);
    ans=work[1].f;
    for(int i=1;i<=n;i++){
        if(ans<=work[i].f)    ans-=work[i].v;
        else    ans=work[i].f-work[i].v;
    }
    if(ans<0)    printf ("-1\n");
    else    printf ("%d\n",ans);
    return 0;
}

洛谷 P2920 [USACO08NOV]時間管理Time Management