P1993 小K的农场
比较裸的差分约束，只是我判负环的时候sb了...
有负环意味着无解
1 #include<iostream> 2 #include<cstdio> 3 #include<queue> 4 #include<algorithm> 5 #include<cmath> 6 #include<ctime> 7 #include<set> 8 #include<map> 9 #include<stack> 10 #include<cstring> 11 #define inf 2147483647 12 #define ls rt<<1 13 #define rs rt<<1|1 14 #define lson ls,nl,mid,l,r 15 #define rson rs,mid+1,nr,l,r 16 #define N 100010 17 #define For(i,a,b) for(register int i=a;i<=b;i++) 18 #define p(a) putchar(a) 19 #define g() getchar() 20 21 using namespace std; 22 23 int n,m; 24 int flag; 25 bool Flag; 26 int x,y,v; 27 int d[100000]; 28 int num[100000]; 29 queue<int>q; 30 bool vis[100000]; 31 32 struct node{ 33 int n; 34 int v; 35 node *next; 36 }*e[1000000]; 37 38 void in(int &x){ 39 int y=1; 40 char c=g();x=0; 41 while(c<'0'||c>'9'){ 42 if(c=='-')y=-1; 43 c=g(); 44 } 45 while(c<='9'&&c>='0'){ 46 x=(x<<1)+(x<<3)+c-'0';c=g(); 47 } 48 x*=y; 49 } 50 void o(int x){ 51 if(x<0){ 52 p('-'); 53 x=-x; 54 } 55 if(x>9)o(x/10); 56 p(x%10+'0'); 57 } 58 59 void push(int x,int y,int v){ 60 node *p; 61 p=new node(); 62 p->n=y; 63 p->v=v; 64 if(e[x]==NULL) 65 e[x]=p; 66 else{ 67 p->next=e[x]->next; 68 e[x]->next=p; 69 } 70 } 71 72 inline void spfa(int x){ 73 if(vis[x]||Flag){ 74 Flag=true; 75 return; 76 } 77 vis[x]=true; 78 for(node *i=e[x];i;i=i->next){ 79 if(Flag) 80 return; 81 if(d[i->n]>d[x]+i->v){ 82 d[i->n]=d[x]+i->v; 83 spfa(i->n); 84 } 85 } 86 vis[x]=false; 87 } 88 89 int main(){ 90 in(n);in(m); 91 For(i,1,m){ 92 in(flag); 93 in(x);in(y); 94 if(flag!=3) 95 in(v); 96 if(flag==1) 97 push(x,y,-v); 98 if(flag==2) 99 push(y,x,v); 100 if(flag==3){ 101 push(x,y,0); 102 push(y,x,0); 103 } 104 } 105 For(i,1,n) 106 push(0,i,0); 107 For(i,1,n) 108 d[i]=inf; 109 spfa(0); 110 if(!Flag) 111 cout<<"Yes"; 112 else 113 cout<<"No"; 114 return 0; 115 }