How Long Does It Take

How Long Does It Take

英文不是很好的我看了好久才知道什么意思

其中我还 调试了一下， 因为没有考虑到多起点， 多终点的情况。考虑到就很简单啦。

除此之外哦，还有就是如何验证图里是否有回路。在这里我用到的是，一个个记录去掉为0的节点，记录他们，

直至没有入度为0的点，然后看看所有的点是否都被记录过，若存在既没有入度为0的点且还有点没被记录过，

则存在回路。

Given the relations of all the activities of a project, you are supposed to find the earliest completion time of the project.

Input Specification:

Each input file contains one test case. Each case starts with a line containing two positive integers N (≤100), the number of activity check points (hence it is assumed that the check points are numbered from 0 to N−1), and M, the number of activities. Then M lines follow, each gives the description of an activity. For the i-th activity, three non-negative numbers are given: S[i], E[i], and L[i], where S[i] is the index of the starting check point, E[i] of the ending check point, and L[i] the lasting time of the activity. The numbers in a line are separated by a space.

Output Specification:

For each test case, if the scheduling is possible, print in a line its earliest completion time; or simply output "Impossible".

Sample Input 1:

9 12
0 1 6
0 2 4
0 3 5
1 4 1
2 4 1
3 5 2
5 4 0
4 6 9
4 7 7
5 7 4
6 8 2
7 8 4

Sample Output 1:

18

Sample Input 2:

4 5
0 1 1
0 2 2
2 1 3
1 3 4
3 2 5

Sample Output 2:

Impossible

#include<iostream> 
#include<vector>
#include<queue>
using namespace std;
#define maxNv 100
#define maxtime 100000
int flag=1;
vector<int> earliest(maxNv,0);
queue<int> q;
vector<int> rudu(maxNv,0);
struct graph{
    int Nv,Ne;
    int G[maxNv][maxNv];
};
using Graph=graph*;
struct enode{
    int v1,v2;
    int time;
};
using edge=enode*;
Graph CreateGraph()
{
    Graph gra=new graph();
    cin>>gra->Nv>>gra->Ne;
    for(int i=0;i<gra->Nv;i++)
    for(int j=0;j<gra->Nv;j++)
    gra->G[i][j]=maxtime;
    return gra;
}
void Insert(edge e,Graph gra){
    gra->G[e->v1][e->v2]=e->time;
    rudu[e->v2]++;
}
Graph BuildGraph(){
    Graph gra=CreateGraph();
    edge e=new enode();
    for(int i=0;i<gra->Ne;i++){
        cin>>e->v1>>e->v2>>e->time;
        Insert(e,gra);
    }
    return gra;
}
void timeset(int v1,Graph gra){
    int f=0;
    for(int i=0;i<gra->Nv;i++)
    if(gra->G[i][v1]!=maxtime&&earliest[i]+gra->G[i][v1]>f)
    f=earliest[i]+gra->G[i][v1];
    earliest[v1]=f;
}
void solve(Graph gra){
    int v1=0,v2=0;
    for(int i=0;i<gra->Nv;i++)
    if(rudu[i]==0) {
    q.push(i);
    earliest[0]=0;    
    }
    while(!q.empty()){
        v1=q.front();
        q.pop();
        rudu[v1]--;
    timeset(v1,gra);
    for(v2=0;v2<gra->Nv;v2++)
    if(gra->G[v1][v2]!=maxtime&&rudu[v2]!=-1){
        rudu[v2]--;
        if(rudu[v2]==0) q.push(v2);}
    }
//    for(int i=0;i<gra->Nv;i++)
//    cout<<rudu[i]<<" ";
//    cout<<endl;
    for(int i=0;i<gra->Nv;i++)
    if(rudu[i]!=-1) flag=0;
    if(flag==0) cout<<"Impossible";
    else{
        int time=-1;
        for(int i=0;i<gra->Nv;i++)
        if(earliest[i]>time) time=earliest[i];
        cout<<time;
    }
}
int main()
{
    Graph gra=BuildGraph();
    solve(gra);
    return 0;
}
} } 
int main() { 
Graph gra=BuildGraph();
 solve(gra);
 return 0; }