洛谷 P1462 通往奥格瑞玛的道路 二分 最短路

Code:

#include<cstdio>
#include<queue>
#include<cstring>
#include<algorithm>
using namespace std;
const long long INF=214748364666;
const int N=10000+2;
const int maxn=50000+3;
queue<int>Q;
long long d[N];
int inq[N];
int cost[N],A[N];
int head[N],to[maxn<<1],nex[maxn<<1],dis[maxn<<1];
int cnt,n,m,b,s,e,diff;
void add_edge(int u,int v,int c)
{
    nex[++cnt]=head[u],head[u]=cnt;
    to[cnt]=v,dis[cnt]=c;
}
void spfa()
{
    for(int i=1;i<=n;++i)d[i]=INF;
    if(cost[s]>diff)return;
    d[s]=0;inq[s]=1;Q.push(s);
    while(!Q.empty())
    {
        int u=Q.front();Q.pop();inq[u]=0;
        for(int v=head[u];v;v=nex[v])
        {
            if(d[u]+dis[v]<d[to[v]]&&cost[to[v]]<=diff)
            {
                d[to[v]]=d[u]+dis[v];
                if(!inq[to[v]])
                {
                    Q.push(to[v]);
                    inq[to[v]]=1;
                }
            }
        }
    }
}
int check(int t)
{
    diff=A[t];
    spfa();
    if(d[e]==INF||d[e]>b)return 0;
    return 1;
}
int main()
{
    //freopen("in.txt","r",stdin);
    scanf("%d%d%d",&n,&m,&b);
    s=1,e=n;
    for(int i=1;i<=n;++i)
    {
        scanf("%d",&cost[i]);
        A[i]=cost[i];
    }
    sort(A+1,A+1+n);
    for(int i=1;i<=m;++i)
    {
        int a,b,c;
        scanf("%d%d%d",&a,&b,&c);
        if(a==b)continue;
        add_edge(a,b,c);
        add_edge(b,a,c);
    }
    int L=1,R=n,ans=-1;
    while(L<=R)
    {
        int mid=(L+R)/2;
        if(check(mid))ans=mid,R=mid-1;
        else L=mid+1;
    }
    if(ans==-1)printf("AFK");
    else printf("%d",A[ans]);
    return 0;
}