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

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:

Sample Output 1:

Sample Input 2:

Sample Output 2:

Impossible

 1 #include<iostream> 
 2 #include<vector>
 3 #include<queue>
 4 using namespace std;
 5 #define maxNv 100
 6 #define maxtime 100000
 7 int flag=1;
 8 vector<int> earliest(maxNv,0);
 9 queue<int> q;
10 vector<int> rudu(maxNv,0);
11 struct graph{
12     int Nv,Ne;
13     int G[maxNv][maxNv];
14 };
15 using Graph=graph*;
16 struct enode{
17     int v1,v2;
18     int time;
19 };
20 using edge=enode*;
21 Graph CreateGraph()
22 {
23     Graph gra=new graph();
24     cin>>gra->Nv>>gra->Ne;
25     for(int i=0;i<gra->Nv;i++)
26     for(int j=0;j<gra->Nv;j++)
27     gra->G[i][j]=maxtime;
28     return gra;
29 }
30 void Insert(edge e,Graph gra){
31     gra->G[e->v1][e->v2]=e->time;
32     rudu[e->v2]++;
33 }
34 Graph BuildGraph(){
35     Graph gra=CreateGraph();
36     edge e=new enode();
37     for(int i=0;i<gra->Ne;i++){
38         cin>>e->v1>>e->v2>>e->time;
39         Insert(e,gra);
40     }
41     return gra;
42 }
43 void timeset(int v1,Graph gra){
44     int f=0;
45     for(int i=0;i<gra->Nv;i++)
46     if(gra->G[i][v1]!=maxtime&&earliest[i]+gra->G[i][v1]>f)
47     f=earliest[i]+gra->G[i][v1];
48     earliest[v1]=f;
49 }
50 void solve(Graph gra){
51     int v1=0,v2=0;
52     for(int i=0;i<gra->Nv;i++)
53     if(rudu[i]==0) {
54     q.push(i);
55     earliest[0]=0;    
56     }
57     while(!q.empty()){
58         v1=q.front();
59         q.pop();
60         rudu[v1]--;
61     timeset(v1,gra);
62     for(v2=0;v2<gra->Nv;v2++)
63     if(gra->G[v1][v2]!=maxtime&&rudu[v2]!=-1){
64         rudu[v2]--;
65         if(rudu[v2]==0) q.push(v2);}
66     }
67 //    for(int i=0;i<gra->Nv;i++)
68 //    cout<<rudu[i]<<" ";
69 //    cout<<endl;
70     for(int i=0;i<gra->Nv;i++)
71     if(rudu[i]!=-1) flag=0;
72     if(flag==0) cout<<"Impossible";
73     else{
74         int time=-1;
75         for(int i=0;i<gra->Nv;i++)
76         if(earliest[i]>time) time=earliest[i];
77         cout<<time;
78     }
79 }
80 int main()
81 {
82     Graph gra=BuildGraph();
83     solve(gra);
84     return 0;
85 }
86 } } 
87 int main() { 
88 Graph gra=BuildGraph();
89  solve(gra);
90  return 0; }

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