POJ 3255 Roadblocks Dijkstra 算法变形

#include <cstdio>
#include <iostream>
#include <queue>

using namespace std;
const int INF = 1000000;

const int maxn = 5005;
struct edge{
	int y,w;
	edge(int cy,int ww){
		y = cy;
		w = ww;
	}
};
vector<edge> vec[maxn];
int n,m;
struct num{
	int d,n;
	bool operator < (const num& a)const{
		return d > a.d;
	}
	num(int x,int y){
		d = x;
		n = y;
	}
};
int d1[maxn];
int d2[maxn];
void fun(){
	priority_queue<num,vector<num>,less<num> > que;
	
	for(int i = 1;i <= n;i++){
		d1[i] = INF;
		d2[i] = INF; 
	}
	d1[1] = 0;
	
	que.push(num(0,1));
	while(!que.empty()){
		num  q = que.top();
		que.pop();
		int u = q.n;
		int d = q.d;
		if(d > d2[u]) continue;
		int cc = vec[u].size();
		for(int i = 0 ; i < cc;i++){
			edge e = vec[u][i];
			int dd2 = d + e.w;
			if(d1[e.y] > dd2){
				swap(d1[e.y],dd2);
				que.push(num(d1[e.y],e.y));
			}
			if(d2[e.y] > dd2 && dd2 > d1[e.y]){
				d2[e.y] = dd2;
				que.push(num(d2[e.y],e.y));
			}
		}
	}
}
int main()
{
	while(scanf("%d%d",&n,&m)!=EOF){
	
		for(int i = 0;i < m;i++){
			int x,y,w;
			scanf("%d%d%d",&x,&y,&w);
			vec[x].push_back(edge(y,w));
			vec[y].push_back(edge(x,w));
		}
	}
	fun();
	printf("%d\n",d2[n]);	
	return 0;