【BZOJ1630】【Usaco2008 Nov】【Time Management 时间管理】【贪心】
2015-10-06 20:43
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Description
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 (likemilking 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.
N个工作,每个工作其所需时间,及完成的Deadline,问要完成所有工作,最迟要什么时候开始.
Input
* Line 1: A single integer: N* Lines 2..N+1: Line i+1 contains two space-separated integers: T_i and S_i
Output
* Line 1: The latest time Farmer John can start working or -1 if Farmer John cannot finish all the jobs on time.Sample Input
43 5
8 14
5 20
1 16
INPUT DETAILS:
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.
Sample Output
2OUTPUT DETAILS:
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.
题解:这个题意真是醉了。。。
看懂题之后从最后结束的时间往前推即可。如果最后的得到的开始时间小于0就输出-1.
代码:
#include<iostream> #include<cstdio> #include<algorithm> using namespace std; struct use{int st,en;}a[1000010]; int n,ans(99999999); bool cmp(use a,use b) {return a.en>b.en;} int main(){ scanf("%d",&n); for (int i=1;i<=n;i++){scanf("%d%d",&a[i].st,&a[i].en);} sort(a+1,a+n+1,cmp); for (int i=1;i<=n;i++)ans=min(ans,a[i].en)-a[i].st; if (ans<0) ans=-1; cout<<ans<<endl; }
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