洛谷负环板子题
差点没笑死我
之前的题解都在清一色diss bfs，吹爆dfs
如今改了数据bfs又崛起了，dfs回家种地了，哈哈哈哈哈
dfs版
1 // luogu-judger-enable-o2 2 #include<iostream> 3 #include<cstdio> 4 #include<queue> 5 #include<algorithm> 6 #include<cmath> 7 #include<ctime> 8 #include<set> 9 #include<map> 10 #include<stack> 11 #include<cstring> 12 #define inf 2147483647 13 #define For(i,a,b) for(register long long i=a;i<=b;i++) 14 #define p(a) putchar(a) 15 #define g() getchar() 16 17 using namespace std; 18 long long T; 19 long long x,y,v; 20 long long n,m; 21 bool flag; 22 bool vis[2010]; 23 long long d[2010]; 24 struct node 25 { 26 long long n; 27 long long v; 28 node *next; 29 }*e[400010]; 30 void in(long long &x) 31 { 32 long long y=1; 33 char c=g();x=0; 34 while(c<'0'||c>'9') 35 { 36 if(c=='-') 37 y=-1; 38 c=g(); 39 } 40 while(c<='9'&&c>='0')x=(x<<1)+(x<<3)+c-'0',c=g(); 41 x*=y; 42 } 43 void o(long long x) 44 { 45 if(x<0) 46 { 47 p('-'); 48 x=-x; 49 } 50 if(x>9)o(x/10); 51 p(x%10+'0'); 52 } 53 54 inline void push(long long x,long long y,long long v) 55 { 56 node *p; 57 p=new node(); 58 p->n=y; 59 p->v=v; 60 if(e[x]==NULL) 61 e[x]=p; 62 else 63 { 64 p->next=e[x]->next; 65 e[x]->next=p; 66 } 67 } 68 69 inline void spfa(long long x) 70 { 71 if(flag)return; 72 if(vis[x]){ 73 flag=true; 74 return; 75 } 76 77 vis[x]=true; 78 for(register node *i=e[x] ;i; i=i->next) 79 { 80 if(flag) 81 return; 82 83 if(d[i->n]>d[x]+i->v){ 84 85 d[i->n]=d[x]+i->v; 86 spfa(i->n); 87 88 } 89 } 90 91 vis[x]=false; 92 } 93 94 int main() 95 { 96 in(T); 97 while(T--) 98 { 99 in(n),in(m); 100 101 For(i,1,n) 102 e[i]=NULL,vis[i]=false,d[i]=inf; 103 flag=false; 104 105 For(i,1,m){ 106 in(x),in(y),in(v); 107 push(x,y,v); 108 if(v>=0) 109 push(y,x,v); 110 } 111 112 d[1]=0; 113 spfa(1); 114 115 if(flag) 116 puts("YE5"); 117 else 118 puts("N0"); 119 } 120 return 0; 121 }
bfs版
1 // luogu-judger-enable-o2 2 #include<iostream> 3 #include<cstdio> 4 #include<queue> 5 #include<algorithm> 6 #include<cmath> 7 #include<ctime> 8 #include<set> 9 #include<map> 10 #include<stack> 11 #include<cstring> 12 #define inf 2147483647 13 #define For(i,a,b) for(register long long i=a;i<=b;i++) 14 #define p(a) putchar(a) 15 #define g() getchar() 16 17 using namespace std; 18 long long T; 19 long long x,y,v; 20 long long n,m; 21 bool flag; 22 bool vis[2010]; 23 long long d[2010]; 24 int num[2010]; 25 26 struct node 27 { 28 long long n; 29 long long v; 30 node *next; 31 }*e[400010]; 32 queue<int>q; 33 34 void in(long long &x) 35 { 36 long long y=1; 37 char c=g();x=0; 38 while(c<'0'||c>'9') 39 { 40 if(c=='-') 41 y=-1; 42 c=g(); 43 } 44 while(c<='9'&&c>='0')x=(x<<1)+(x<<3)+c-'0',c=g(); 45 x*=y; 46 } 47 void o(long long x) 48 { 49 if(x<0) 50 { 51 p('-'); 52 x=-x; 53 } 54 if(x>9)o(x/10); 55 p(x%10+'0'); 56 } 57 58 inline void push(long long x,long long y,long long v) 59 { 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 { 68 p->next=e[x]->next; 69 e[x]->next=p; 70 } 71 } 72 73 inline void spfa(long long x){ 74 q.push(x); 75 vis[x]=true; 76 num[1]++; 77 while(!q.empty()){ 78 int t=q.front();q.pop(); 79 vis[t]=true; 80 for(node *i=e[t];i;i=i->next){ 81 82 if(d[i->n]>d[t]+i->v){ 83 d[i->n]=d[t]+i->v; 84 num[i->n]++; 85 if(num[i->n]>=n){ 86 flag=true; 87 return; 88 } 89 if(!vis[i->n]){ 90 q.push(i->n); 91 vis[i->n]=true; 92 93 } 94 } 95 96 } 97 vis[t]=false; 98 } 99 } 100 101 int main() 102 { 103 in(T); 104 while(T--) 105 { 106 in(n),in(m); 107 108 For(i,1,n) 109 e[i]=NULL,vis[i]=false,d[i]=inf,num[i]=0; 110 while(!q.empty()) 111 q.pop(); 112 flag=false; 113 114 For(i,1,m){ 115 in(x),in(y),in(v); 116 push(x,y,v); 117 if(v>=0) 118 push(y,x,v); 119 } 120 121 d[1]=0; 122 spfa(1); 123 124 if(flag) 125 puts("YE5"); 126 else 127 puts("N0"); 128 } 129 return 0; 130 }