UVALive 6885 spfa

来源：互联网发布：易建联巅峰赛季数据编辑：程序博客网时间：2024/05/06 07:52
#include<stdio.h>#include<algorithm>#include<string.h>#include<vector>#include<queue>using namespace std;const int inf=0x7fffffff;const int N=10000+5;int p,t,f1[N],f2[N],dis1[N],dis2[N];struct{    int u,v,c;}edge[250000+5];vector<int>g[10000+5];void spfa1(){    queue<int>q;    int i,u,v,k;    memset(f1,0,sizeof(f1));    for(i=0;i<p;i++)        dis1[i]=inf;    dis1[0]=0;    q.push(0);    while(!q.empty())    {        u=q.front();        q.pop();        f1[u]=0;        for(i=0;i<g[u].size();i++)        {            k=g[u][i];            if(edge[k].u==u)            {                v=edge[k].v;                if(dis1[u]+edge[k].c<=dis1[v])                {                    dis1[v]=dis1[u]+edge[k].c;                    if(f1[v]==0)                    {                        f1[v]=1;                        q.push(v);                    }                }            }            else if(edge[k].v==u)            {                v=edge[k].u;                if(dis1[u]+edge[k].c<=dis1[v])                {                    dis1[v]=dis1[u]+edge[k].c;                    if(f1[v]==0)                    {                        f1[v]=1;                        q.push(v);                    }                }            }        }    }}void spfa2(){    queue<int>q;    int i,u,v,k;    memset(f2,0,sizeof(f2));    for(i=0;i<p;i++)        dis2[i]=inf;    dis2[p-1]=0;    q.push(p-1);    while(!q.empty())    {        u=q.front();q.pop();        f2[u]=0;        for(i=0;i<g[u].size();i++)        {            k=g[u][i];            if(edge[k].u==u)            {                v=edge[k].v;                if(dis2[u]+edge[k].c<=dis2[v])                {                    dis2[v]=dis2[u]+edge[k].c;                    if(f2[v]==0)                    {                        f2[v]=1;                        q.push(v);                    }                }            }            else if(edge[k].v==u)            {                v=edge[k].u;                if(dis2[u]+edge[k].c<=dis2[v])                {                    dis2[v]=dis2[u]+edge[k].c;                    if(f2[v]==0)                    {                        f2[v]=1;                        q.push(v);                    }                }            }        }    }}int main(){    int i,dis,ans,u,v,c;    while(~scanf("%d%d",&p,&t))    {        for(i=0;i<p;i++)            g[i].clear();        for(i=0;i<t;i++)        {            scanf("%d%d%d",&u,&v,&c);            edge[i].u=u;            edge[i].v=v;            edge[i].c=c;            g[u].push_back(i);            g[v].push_back(i);        }        spfa1();        spfa2();        dis=dis1[p-1];        ans=0;        //for(i=0;i<p;i++) printf("%d ",dis1[i]);        for(i=0;i<t;i++)        {            u=edge[i].u;            v=edge[i].v;            c=edge[i].c;            if(dis1[u]+dis2[v]+c==dis||dis1[v]+dis2[u]+c==dis)                ans+=c;        }        printf("%d\n",2*ans);    }    return 0;}
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