P1462 通往奥格瑞玛的道路

Miku

---

一个小小二分+spfa

二分经过的最贵的点，然后跑spfa判断行不行。

没啥思维难度

#include<iostream>
#include<cstdio>
#include<algorithm>
#include<cstring>
#include<queue> 
#define int long long
using namespace std;
int n,m;
int b;
int f[100001];
struct b{
	int f,t,v;
	int ne;
}ed[5000001];
int vis[100001];
int l,r;
queue <int> q;
int p;
int head[100001];
int dis[100001];
void add(int f,int t,int v){
	p++;
	ed[p].f=f;
	ed[p].t=t;
	ed[p].v=v;
	ed[p].ne=head[f];
	head[f]=p;
	return ;
}
int x,y,z;
int check(int x){
	memset(vis,0,sizeof(vis));
	memset(dis,0x3f,sizeof(dis));
	q.push(1);
	vis[1]=1;
	dis[1]=0;
	while(!q.empty()){
		int u=q.front();
		q.pop();
		vis[u]=0;
		for(int i=head[u];i;i=ed[i].ne){
			int v=ed[i].t;
			if(f[v]>x)
			continue;
			if(dis[v]>dis[u]+ed[i].v){
				dis[v]=dis[u]+ed[i].v;
				if(!vis[v])
				q.push(v);
			}
		}
	}
	return dis[n]<=b ? 1 : 0;
}
signed main(){
	scanf("%lld%lld%lld",&n,&m,&b);
	for(int i=1;i<=n;++i){
		scanf("%lld",&f[i]);
	}
	for(int i=1;i<=m;++i){
		scanf("%lld%lld%lld",&x,&y,&z);
		add(x,y,z);
		add(y,x,z);
	}
	int l=1;r=1000001001;
	while(l<=r){
		int mid=l+(r-l)/2;
		if(check(mid))
		r=mid-1;
		else
		l=mid+1;	
	}
	if(l==1000001002)
	cout<<"AFK";
	else
	cout<<l<<endl;
	
	return 0;
}