学习SPFA，正好是裸的SPFA，然后我就学习了一下。
1 #include <iostream> 2 #include <stdio.h> 3 #include <math.h> 4 #include <queue> 5 #include <string.h> 6 #define maxn 600 7 #define INF 0x7fffffff 8 using namespace std; 9 struct node { 10 int to; 11 int weight; 12 node* next; 13 }; 14 node* LIST[maxn]; 15 queue<int>Q; 16 int dist[maxn],inq[maxn],count1[maxn],path[maxn]; 17 bool SPFA(int begin,int n); 18 int main() 19 { 20 int n,m,w; 21 int i,j; 22 int t; 23 int t1,t2,t3; 24 node* temp; 25 while(~scanf("%d",&t)){ 26 while(t--){ 27 scanf("%d%d%d",&n,&m,&w); 28 memset(LIST,0,sizeof(LIST)); 29 while(m--){ 30 scanf("%d%d%d",&t1,&t2,&t3); 31 temp=new node; 32 temp->to=t2; temp->weight=t3; temp->next=NULL; 33 if(LIST[t1]==NULL) 34 LIST[t1]=temp; 35 else 36 temp->next=LIST[t1],LIST[t1]=temp; 37 temp=new node; 38 temp->to=t1; temp->weight=t3; temp->next=NULL; 39 if(LIST[t2]==NULL) 40 LIST[t2]=temp; 41 else 42 temp->next=LIST[t2],LIST[t2]=temp; 43 } 44 while(w--){ 45 scanf("%d%d%d",&t1,&t2,&t3); 46 temp=new node; 47 temp->to=t2; temp->weight=-t3; temp->next=NULL; 48 if(LIST[t1]==NULL) 49 LIST[t1]=temp; 50 else 51 temp->next=LIST[t1],LIST[t1]=temp; 52 } 53 54 if(SPFA(1,n)) 55 printf("YES\n"); 56 else 57 printf("NO\n"); 58 for(i=1;i<=n;++i){ 59 temp=LIST[i]; 60 while(temp!=NULL){ 61 LIST[i]=temp->next; delete temp; temp=LIST[i]; 62 } 63 } 64 } 65 } 66 return 0; 67 } 68 bool SPFA(int begin,int n) 69 { 70 memset(inq,0,sizeof(inq)); 71 memset(count1,0,sizeof(count1)); 72 while(!Q.empty()) 73 Q.pop(); 74 int i,u; 75 for(i=1;i<=n;++i) 76 dist[i]=INF,path[i]=begin,inq[i]=0; 77 node* temp; 78 dist[begin]=0,inq[begin]++; 79 Q.push(begin),count1[begin]++; 80 while(!Q.empty()){ 81 u=Q.front(); 82 Q.pop(); 83 inq[u]--; 84 if(count1[u]>n) 85 return true; 86 temp=LIST[u]; 87 while(temp!=NULL){ 88 int v=temp->to; 89 if(dist[v]>dist[u]+temp->weight){ 90 dist[v]=dist[u]+temp->weight,path[v]=u; 91 if(!inq[v]){ 92 Q.push(v); count1[v]++; inq[v]++; 93 } 94 } 95 temp=temp->next; 96 } 97 } 98 return false; 99 } 100 101 102 103 104 105 106