感觉去年9月的自己好$naive$ http://www.cnblogs.com/candy99/p/5868948.html
现在不也是嘛
裸题,具体看学习笔记
二分答案之后判负环就行了
$dfs$版超快
#include <iostream> #include <cstdio> #include <algorithm> #include <cstring> #include <queue> using namespace std; typedef long long ll; const int N=1005,M=5005; const double eps=1e-4; inline int read(){ char c=getchar();int x=0,f=1; while(c<‘0‘||c>‘9‘){if(c==‘-‘)f=-1;c=getchar();} while(c>=‘0‘&&c<=‘9‘){x=x*10+c-‘0‘;c=getchar();} return x*f; } int n,m,u,v; double f[N]; struct edge{ int v,ne; double w; }e[M<<1]; int h[N],cnt=0; inline void ins(int u,int v,int w){ cnt++; e[cnt].v=v;e[cnt].w=w;e[cnt].ne=h[u];h[u]=cnt; } double d[N]; int inq[N],num[N]; int q[N],head,tail; inline void lop(int &x){if(x==N) x=1;} bool NegativeCircle(double mid){ head=tail=0; for(int i=1;i<=n;i++) d[i]=0,inq[i]=1,q[tail++]=i,num[i]=1; while(head!=tail){ int u=q[head++];lop(head);inq[u]=0; for(int i=h[u];i;i=e[i].ne){ int v=e[i].v;double w=mid*e[i].w-f[u]; if(d[v]>d[u]+w){ d[v]=d[u]+w; if(!inq[v]){ inq[v]=1;q[tail++]=v;lop(tail); if(++num[v]>n) return true; } } } } return false; } inline bool check(double mid){return NegativeCircle(mid);} void solve(){ double l=0,r=2000; while(r-l>eps){ double mid=(l+r)/2.0; if(check(mid)) l=mid; else r=mid; } printf("%.2f",l); } int main(){ freopen("in","r",stdin); n=read();m=read(); for(int i=1;i<=n;i++) f[i]=read(); for(int i=1;i<=m;i++) u=read(),v=read(),ins(u,v,read()); solve(); }
#include <iostream> #include <cstdio> #include <algorithm> #include <cstring> #include <queue> using namespace std; typedef long long ll; const int N=1005,M=5005; const double eps=1e-4; inline int read(){ char c=getchar();int x=0,f=1; while(c<‘0‘||c>‘9‘){if(c==‘-‘)f=-1;c=getchar();} while(c>=‘0‘&&c<=‘9‘){x=x*10+c-‘0‘;c=getchar();} return x*f; } int n,m,u,v; double f[N]; struct edge{ int v,ne; double w; }e[M<<1]; int h[N],cnt=0; inline void ins(int u,int v,int w){ cnt++; e[cnt].v=v;e[cnt].w=w;e[cnt].ne=h[u];h[u]=cnt; } double d[N]; int vis[N],cl; bool dfs(int u,double mid){ vis[u]=cl; for(int i=h[u];i;i=e[i].ne){ int v=e[i].v;double w=mid*e[i].w-f[u]; if(d[v]>d[u]+w){ d[v]=d[u]+w; if(vis[v]==vis[u]) return true; else if(dfs(v,mid)) return true; } } vis[u]=0; return false; } bool NegativeCircle(double mid){ memset(vis,0,sizeof(vis)); for(cl=1;cl<=n;cl++) if(dfs(cl,mid)) return true; return false; } inline bool check(double mid){return NegativeCircle(mid);} void solve(){ double l=0,r=2000; while(r-l>eps){ double mid=(l+r)/2.0; if(check(mid)) l=mid; else r=mid; } printf("%.2f",l); } int main(){ freopen("in","r",stdin); n=read();m=read(); for(int i=1;i<=n;i++) f[i]=read(); for(int i=1;i<=m;i++) u=read(),v=read(),ins(u,v,read()); solve(); }
时间: 2024-10-25 14:54:03