08-图8 How Long Does It Take

 1 //拓扑排序 
 2 #include<stdio.h>
 3 #include<stdlib.h>
 4 #define Max 105
 5 #define ERROR -1
 6 
 7 int N, M;
 8 int Graph[Max][Max];        //邻接矩阵储存图 
 9 int Indegree[Max] = {0};    //记录每个结点的入度 
10 int time[Max] = {0};        //记录每个结点需要花费的时间 
11 
12 void init(){
13     for(int i=0; i<N; i++){
14         for(int j=0; j<N; j++){
15             Graph[i][j] = ERROR;
16         }
17     }
18 }
19 
20 void BuildG(){
21     scanf("%d%d", &N, &M);
22     init();
23     for(int i=0; i<M; i++){
24         int S, E, time;
25         scanf("%d%d%d", &S, &E, &time);
26         Graph[S][E] = time;
27         Indegree[E]++;
28     }
29 }
30 
31 typedef struct QNode{
32     int *data;
33     int rear, front;
34     int maxsize;
35 }*Queue;
36 
37 Queue BuildQ(){
38     Queue Q = (Queue)malloc(sizeof(struct QNode));
39     Q->data = (int *)malloc(sizeof(int)*N);
40     Q->front = Q->rear = 0;
41     Q->maxsize = N;
42     return Q;
43 }
44 
45 void AddQ(Queue Q, int x){
46     Q->rear = (Q->rear + 1)%Q->maxsize;
47     Q->data[Q->rear] = x;
48 }
49 
50 bool IsEmpty(Queue Q){
51     return Q->front == Q->rear;
52 }
53 
54 int DeleteQ(Queue Q){
55     Q->front = (Q->front + 1)%Q->maxsize;
56     return Q->data[Q->front];
57 }
58 
59 void TopSort(){
60     Queue Q = BuildQ();          //用队列记录入度为0的结点 
61     for(int i=0; i<N; i++){
62         if(Indegree[i]==0){
63             AddQ(Q, i);
64         }
65     }
66     int v, cnt=0, Time;
67     while(!IsEmpty(Q)){
68         v = DeleteQ(Q);
69         cnt++;
70         for(int i=0; i<N; i++){
71             if(Graph[v][i]!=ERROR){
72                 Indegree[i]--;
73                 if(Indegree[i]==0){
74                     AddQ(Q, i);
75                 }
76                 if(time[v] + Graph[v][i] > time[i]){
77                     time[i] = time[v] + Graph[v][i];
78                 }
79                 if(time[i]>Time){
80                     Time = time[i];
81                 }
82             } 
83         }
84     }
85     if(cnt<N){      //如果有几个结点不能被出队，则一定存在闭环，输出impossible 
86         printf("Impossible\n");
87     }
88     else printf("%d\n", Time);
89 }
90 
91 int main(){
92     BuildG();
93     TopSort();
94     return 0;
95 }