UVA - 10986 Sending email （Dijkstra邻接表+优先队列优化）

题目大意:
给一个图， 求从s点到t点的最小距离。

解析：
赤裸裸的最短路，但n太大显然是不能用邻接矩阵的，需要对Dijkstra用邻接表+优先队列优化。

这里我把Dijkstra的邻接表+优先队列的方法封装成了一个类，感觉挺好用的。

#include <cstdio>
#include <cstring>
#include <vector>
#include <algorithm>
#include <queue>
using namespace std;
const int INF = 0x3f3f3f3f;
const int maxn = 20005;
struct Edge {
	int from, to, dist;
	Edge(int u,int v,int d) {
		from = u;
		to = v;
		dist = d;
	}
};
struct HeapNode {
	int d, u;
	HeapNode(int _d,int _u) {
		d = _d;
		u = _u;
	}
	bool operator < (const HeapNode& rhs) const {
		return d > rhs.d;
	}
};
struct Dijkstra {
	int n,m;
	vector<Edge> edges;
	vector<int> G[maxn];
	
	bool done[maxn]; //是否被永久标记
	int d[maxn]; //s到各个点的距离
	int p[maxn]; //最短路上的一条弧
	
	void init(int n) {
		this->n = n;
		for(int i = 0; i < n; i++) {
			G[i].clear();
		}
		edges.clear();
	}
	
	void AddEdge(int from,int to,int dist) {
		edges.push_back(Edge(from,to,dist));
		m = edges.size();
		G[from].push_back(m-1);
	}

	void dijkstra(int s) {
		priority_queue<HeapNode> Q;
		for(int i = 0; i < n; i++) {
			d[i] = INF;
		}
		d[s] = 0;
		memset(done,0,sizeof(done));
		Q.push(HeapNode(0,s));
		while(!Q.empty()) {
			HeapNode x = Q.top();
			Q.pop();
			int u = x.u;
			if(done[u]) {
				continue;
			}
			done[u] = true;
			for(int i = 0; i < G[u].size(); i++) {
				Edge& e = edges[G[u][i]];
				if(d[e.to] > d[u] + e.dist) {
					d[e.to] = d[u] + e.dist;
					p[e.to] = G[u][i];
					Q.push(HeapNode(d[e.to], e.to));
				}
			}
		}
	}
};

int main() {
	Dijkstra dij;
	int t,cas = 1;
	int n,m;
	int u,v,dist;
	int s,e;
	scanf("%d",&t);
	while(t--) {
		scanf("%d%d%d%d",&n,&m,&s,&e);
		dij.init(n);
		for(int i = 0; i < m; i++) {
			scanf("%d%d%d",&u,&v,&dist);
			dij.AddEdge(u,v,dist);
			dij.AddEdge(v,u,dist);
		}
		dij.dijkstra(s);
		printf("Case #%d: ",cas++);
		if(dij.d[e] == INF) {
			printf("unreachable\n");	
		}else {
			printf("%d\n",dij.d[e]);
		}
	}
	return 0;
}