BZOJ 1631: [Usaco2007 Feb]Cow Party

来源：互联网发布：java.util在哪个jar包编辑：程序博客网时间：2024/05/29 18:42

用边建正反俩张图
然后拍spfa计算两张图从x点出发的最短路。。
然后扫一遍计算答案
像我这样把两张图连起来跑一次spfa也行

#include<cstdio>#include<cstring>#include<cmath>#include<algorithm>#define ll long long#define g getchar()#define inf 0x3f3f3f3f#define rep(i,n) for(int i=1;i<=n;++i)using namespace std;inline ll read(){    ll x=0,f=1;char ch=g;    for(;ch<'0'||ch>'9';ch=g)if(ch=='-')f=-1;    for(;ch>='0'&&ch<='9';ch=g)x=x*10+ch-'0';    return x*f;}inline void out(ll x){    int a[25],t=0;    if(x<0)putchar('-'),x=-x;    for(;x;x/=10)a[++t]=x%10;    for(int i=t;i;--i)putchar('0'+a[i]);    if(t==0)putchar('0');    putchar('\n');}struct re{int v,w,next;}ed[200005];int dis[2005],pd[2005],dui[200005],head[2005],n,m,T,e,ans;inline void ins(int x,int y,int w){ed[++e]=(re){y,w,head[x]};head[x]=e;}void spfa(int S){    memset(dis,inf,sizeof(dis));    memset(pd,0,sizeof(pd));    dis[S]=0;dui[1]=S;int tou=1,wei=1;    for(;tou<=wei;pd[dui[tou++]]=0){        int u=dui[tou];        for(int i=head[u];i;i=ed[i].next){            int v=ed[i].v;            if(dis[v]>dis[u]+ed[i].w){                dis[v]=dis[u]+ed[i].w;                if(!pd[v])dui[++wei]=v,pd[v]=1;            }        }    }}int main(){//  freopen("","r",stdin);//  freopen("","w",stdout);    n=read(),m=read(),T=read();    rep(i,m){        int x=read(),y=read(),w=read();        ins(x,y,w);        ins(y+n,x+n,w);    }    ins(T,T+n,0);    spfa(T);    rep(i,n){        ans=max(dis[i]+dis[i+n],ans);    }    out(ans);    return 0;}

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