P1462 通往奥格瑞玛的道路

二分答案，大于二分值的边直接不走，看最后是否存在一条路径即可

#include <algorithm>
#include <iostream>
#include <cstring>
#include <cstdio>
#include <queue>
using namespace std;
#define debug(x) cerr << #x << "=" << x << endl;
const int MAXN = 10000 + 10;
const int MAXM = 500000 + 10;
int n,m,last[MAXN],tot,dist[MAXN],s,vis[MAXN],g[MAXN],f[MAXN],b;
queue <int> q;
struct Edge{
	int u,v,w,to;
	Edge(){}
	Edge(int u, int v, int w, int to) : u(u), v(v), w(w), to(to) {}
}e[MAXM];
inline void add(int u, int v, int w) {
	e[++tot] = Edge(u,v,w,last[u]);
	last[u] = tot;
}
bool SPFA(int s) {
	memset(dist,0x3f,sizeof(dist));
	memset(vis,0,sizeof(vis));
	dist[1] = 0;
	q.push(1);
	vis[1] = 1;
	while(!q.empty()) {
		int x = q.front();
		q.pop();
		vis[x] = 0;
		for(int i=last[x]; i; i=e[i].to) {
			int v = e[i].v;
			int w = e[i].w;
			if(dist[v] > dist[x] + w) {
				if(f[v] <= s) {
					dist[v] = dist[x] + w;
					if(!vis[v]) q.push(v), vis[v] = 1;
				}
			}
		}
	}
	if(dist[n] >= b) return false;
	else return true;
}
int main() {
	cin >> n >> m >> b;
	for(int i=1; i<=n; i++) {
		cin >> f[i];
		g[i] = f[i];
	}
	for(int i=1; i<=m; i++) {
		int a,b,c;
		cin >> a >> b >> c;
		add(a,b,c);
		add(b,a,c);
	}
	int l=1, r = n;
	sort(g+1,g+n+1);
	int ans=0;
	int mid;
	if(!SPFA(1<<30)) {
		cout << "AFK" << endl;
		return 0;
	}
	while(l <= r) {
		mid = l+r>>1;
		if(SPFA(g[mid])) {
			ans = g[mid];
			r = mid-1;
		} else {
			l = mid+1;
		}
	}
	cout << ans;
	return 0;
}