一本通1498：Roadblocks

#include <cstdio>
#include <cstring>
#include <queue>
#include <algorithm>
#include<functional>
#define MAXN (5000 + 10)
#define INF (5000*5000*2)
using namespace std;

struct edge {
    int to, cost;
	edge(int tv = 0, int tc = 0) :
		to(tv), cost(tc) {}
};
typedef pair<int, int> P;
int N, R;
vector<edge> graph[MAXN];

int dist[MAXN];     
int dist2[MAXN];    

void solve() {
	fill(dist, dist + N, INF);
	fill(dist2, dist2 + N, INF);
	priority_queue<P, vector<P>, greater<P> > Q;
	
	dist[0] = 0;
	Q.push(P(0, 0));
	
	while (!Q.empty()) {
		P p = Q.top(); Q.pop();	
		int v = p.second, d = p.first;	
		if (dist2[v] < d) 
			continue;


		for (unsigned i = 0; i < graph[v].size(); i++) {
			edge &e = graph[v][i];
			int d2 = d + e.cost;
			if (dist[e.to] > d2) {
				swap(dist[e.to], d2);
				Q.push(P(dist[e.to], e.to));
			}
			if (dist2[e.to] > d2 && dist[v] < d2) {
				dist2[e.to] = d2;
				Q.push(P(dist2[e.to], e.to));
			}
		}
	}
	printf("%d\n", dist2[N - 1]);
}

int main() {
	int A, B, D;
	scanf("%d%d", &N, &R);
	for (int i = 0; i < R; i++) {
		scanf("%d%d%d", &A, &B, &D);
		graph[A - 1].push_back(edge(B - 1, D));
		graph[B - 1].push_back(edge(A - 1, D));
	}
	solve();
	//while(1){}
	return 0;
}