1 #include <stdlib.h> 
  2 #include <cstdio>
  3 #include <queue>
  4 #define MaxVertexNum 102
  5 #define INFINITY 65536
  6 using namespace std;
  7 
  8 typedef int Vertex;         
  9 typedef int WeightType;        
 10 typedef int DataType;       
 11 
 12 int Indegree[MaxVertexNum];
 13 
 14 
 15 typedef struct ENode *Edge;
 16 struct ENode{
 17     Vertex V1, V2;      
 18     WeightType Weight;  
 19 };
 20 
 21 typedef struct AdjVNode *PtrToAdjVNode; 
 22 struct AdjVNode{
 23     Vertex AdjV;       
 24     WeightType Weight;  
 25     PtrToAdjVNode Next;   
 26 };
 27  
 28 typedef struct Vnode{
 29     PtrToAdjVNode FirstEdge;
 30     DataType Data;            
 31 } AdjList[MaxVertexNum];    /* AdjListÊÇÁÚ½Ó±íÀàÐÍ */
 32  
 33  
 34 
 35 typedef struct GNode *LGraph;
 36 struct GNode{  
 37     int Nv;     
 38     int Ne;     
 39     AdjList G; 
 40 };
 41 
 42 
 43 
 44 LGraph CreateGraph( int VertexNum );
 45 void InsertEdge( LGraph Graph, Edge E );
 46 LGraph BuildGraph();
 47 bool topSort(LGraph Graph);
 48 
 49 void find_max(LGraph Graph);
 50 
 51 int main() {
 52     LGraph Graph = BuildGraph();
 53     
 54     if( !topSort(Graph) ) printf("Impossible\n");
 55     else {
 56         find_max(Graph);
 57     }
 58 
 59     
 60 }
 61 
 62 LGraph CreateGraph( int VertexNum )
 63 { 
 64     Vertex V;
 65     LGraph Graph;
 66      
 67     Graph = (LGraph)malloc( sizeof(struct GNode) ); 
 68     Graph->Nv = VertexNum;
 69     Graph->Ne = 0;
 70     
 71        for (V=0; V<Graph->Nv; V++)
 72         Graph->G[V].FirstEdge = NULL;
 73              
 74     return Graph; 
 75 }      
 76 void InsertEdge( LGraph Graph, Edge E )
 77 {
 78     PtrToAdjVNode newNode = new AdjVNode;
 79     newNode->Weight = E->Weight;
 80     newNode->AdjV = E->V2;
 81     
 82     newNode->Next = Graph->G[E->V1].FirstEdge;
 83     Graph->G[E->V1].FirstEdge = newNode;
 84          
 85 
 86 }
 87 LGraph BuildGraph()
 88 {
 89     LGraph Graph;
 90     int Nv;
 91     Edge E;
 92     Vertex V;
 93     
 94     scanf("%d", &Nv);
 95     Graph = CreateGraph(Nv);
 96     
 97     scanf("%d", &(Graph->Ne));
 98     
 99     if(Graph->Ne) {
100         E = new ENode;
101         for(int i=0; i<Graph->Ne; i++) {
102             scanf("%d %d %d", &(E->V1), &(E->V2), &(E->Weight));
103             InsertEdge(Graph, E);
104         } 
105     }
106     
107     for(V=0; V<Graph->Nv; V++) {
108         Graph->G[V].Data = 0;
109     }
110     return Graph;
111   
112 }
113 bool topSort(LGraph Graph) 
114 {
115     int cnt;
116     Vertex V;
117     queue<Vertex> Q;
118     
119     cnt = 0;
120     for( V=0; V<Graph->Nv; V++) Indegree[V] = 0;
121     
122     for( V = 0; V < Graph->Nv; V++) {
123         for(PtrToAdjVNode W = Graph->G[V].FirstEdge; W; W=W->Next) {
124             Indegree[W->AdjV]++;
125             Graph->G[W->AdjV].Data = 0;
126         }
127     }
128     for(V=0; V<Graph->Nv; V++) if(Indegree[V] == 0) Q.push(V);
129     
130     while(!Q.empty()) {
131         V = Q.front();
132         Q.pop();
133         cnt++;
134         
135         for(PtrToAdjVNode W = Graph->G[V].FirstEdge; W; W=W->Next) {
136             if(--Indegree[W->AdjV] == 0) Q.push(W->AdjV);
137             if(Graph->G[W->AdjV].Data < W->Weight + Graph->G[V].Data) 
138                 Graph->G[W->AdjV].Data =  W->Weight + Graph->G[V].Data;
139             
140         }
141         
142         
143     }
144     
145     if(cnt != Graph->Nv) return false;
146     return true;
147     
148 
149 }
150 
151 void find_max(LGraph Graph)
152 {
153     Vertex V;
154     int compTime;
155     compTime = Graph->G[0].Data;
156     
157     for(V = 1; V < Graph->Nv; V++) {
158         if(Graph->G[V].Data > compTime) compTime = Graph->G[V].Data;
159     }
160     printf("%d\n", compTime);
161 }