bzoj1631 [Usaco2007 Feb]Cow Party(Dijkstra)

心情烦躁只好刷水题。。。正反两遍最短路即可。。

#include <bits/stdc++.h>using namespace std;#define N 1010#define M 100010#define ll long long#define inf 0x3f3f3f3f#define pa pair<int,int>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=x*10+ch-'0',ch=getchar();    return x*f;}int n,m,s,h[N],h1[N],num=0,d[N],d1[N],ans=0;bool f[N];struct edge{    int to,from,next,next1,val;}data[M];void Dijkstra(){    priority_queue<pa,vector<pa>,greater<pa> >q;    memset(d,0x3f,sizeof(d));    q.push(make_pair(0,s));d[s]=0;    while(!q.empty()){        int x=q.top().second;q.pop();        if(f[x]) continue;f[x]=1;        for(int i=h[x];i;i=data[i].next){            int y=data[i].to;            if(d[x]+data[i].val<d[y]){                d[y]=d[x]+data[i].val;q.push(make_pair(d[y],y));            }        }    }}void Dijkstra1(){    priority_queue<pa,vector<pa>,greater<pa> >q;    memset(d1,0x3f,sizeof(d1));memset(f,0,sizeof(f));    q.push(make_pair(0,s));d1[s]=0;    while(!q.empty()){        int x=q.top().second;q.pop();        if(f[x]) continue;f[x]=1;        for(int i=h1[x];i;i=data[i].next1){            int y=data[i].from;            if(d1[x]+data[i].val<d1[y]){                d1[y]=d1[x]+data[i].val;q.push(make_pair(d1[y],y));            }        }    }}int main(){//  freopen("a.in","r",stdin);    n=read();m=read();s=read();    while(m--){        int x=read(),y=read(),val=read();        data[++num].to=y;data[num].next=h[x];h[x]=num;data[num].val=val;        data[num].from=x;data[num].next1=h1[y];h1[y]=num;    }    Dijkstra();Dijkstra1();    for(int i=1;i<=n;++i) ans=max(ans,d[i]+d1[i]);    printf("%d\n",ans);    return 0;}