BZOJ1179: [Apio2009]Atm

1179: [Apio2009]Atm

Time Limit: 15 Sec Memory Limit: 162 MB
Submit: 1427 Solved: 544
[Submit][Status]

Description

#include<cstdio>
#include<cstdlib>
#include<cmath>
#include<cstring>
#include<algorithm>
#include<iostream>
#include<vector>
#include<map>
#include<set>
#include<queue>
#define inf 1000000000
#define maxn 500000+10000
#define maxm 500+100
#define eps 1e-10
#define ll long long
using namespace std;
inline int read()
{
int x=0,f=1;char ch=getchar();
while(ch<'0'||ch>'9'){if(ch=='-')f=-1;ch=getchar();}
while(ch>='0'&&ch<='9'){x=10*x+ch-'0';ch=getchar();}
return x*f;
}
int n,m,ss,p,cnt,tot,ti,top,head[maxn],low[maxn],dfn[maxn],scc[maxn];
int sta[maxn],from[maxn],go[maxn],q[2*maxn],a[maxn];
ll ans,s[maxn],d[maxn];
bool b[maxn],c[maxn],v[maxn];

struct edge{int go,next;}e[maxn];
void insert(int x,int y)
{
e[++tot].go=y;e[tot].next=head[x];head[x]=tot;
}
void dfs(int x)
{
int y;
low[x]=dfn[x]=++ti;sta[++top]=x;
for(int i=head[x];i;i=e[i].next)
if (!dfn[y=e[i].go])
{
dfs(y);
low[x]=min(low[x],low[y]);
}
else if(!scc[y])low[x]=min(low[x],dfn[y]);
if(low[x]==dfn[x])
{
cnt++;
while(1)
{
scc[y=sta[top--]]=cnt;s[cnt]+=a[y];
if(b[y])c[cnt]=1;
if(y==x)break;
}
}
}
void tarjan()
{
for(int i=1;i<=n;i++)if(!dfn[i])dfs(i);
}
void spfa()
{
for(int i=1;i<=cnt;++i) d[i]=0;
memset(v,0,sizeof(v));
int l=0,r=1,x,y;q[1]=scc[ss];d[scc[ss]]=s[scc[ss]];
while(l!=r)
{
x=q[++l];if(l==maxn)l=0;v[x]=0;
for(int i=head[x];i;i=e[i].next)
if(d[x]+s[y=e[i].go]>d[y])
{
d[y]=d[x]+s[y];
if(!v[y]){v[y]=1;q[++r]=y;if(r==maxn)r=0;}
}
}
}
int main()
{
freopen("input.txt","r",stdin);
freopen("output.txt","w",stdout);
n=read();m=read();
int x,y;
for(int i=1;i<=m;i++)from[i]=read(),go[i]=read(),insert(from[i],go[i]);
for(int i=1;i<=n;i++)a[i]=read();
ss=read();p=read();
for(int i=1;i<=p;i++)x=read(),b[x]=1;
tarjan();
memset(head,0,sizeof(head));tot=0;
for(int i=1;i<=m;i++)
if(scc[x=from[i]]!=scc[y=go[i]])
{
insert(scc[x],scc[y]);
}
spfa();
ans=0;
for(int i=1;i<=cnt;i++)if(c[i])ans=max(ans,d[i]);
printf("%lld\n",ans);
return 0;
}

View Code

UPD:为何现在看着这题觉得不应该SPFA，而是应该拓扑排序之后求个最长链什么的，又因为限制了起点，所以可以对事先入队的节点的函数值动手脚就行了23