TOJ 1883 ZOJ 1298 POJ 1135 Domino Effect / Dijkstra

把第一个推倒 求所有多米诺倒下的最短时间 不是每个点上有一个骨牌 是路上都有 每个点只是关键的骨牌

只有一种最优解 先求出1到各点的最短路 求最短路中的最大值 这是一个关键点的情况

在枚举每一条边 u v w 如果(d[u] + d[v] + w) / 2 > max 就更新一下 因为是要求最短路的最大值  这是2个关键点的情况

Dijkstra

#include <cstring>
#include <cstdio>
#include <vector>
#include <queue>
using namespace std;
const int maxn = 510;
const double INF = 999999999;

struct HeapNode
{
	double d;
	int u;
	bool operator < (const HeapNode& rhs) const
	{
		return d > rhs.d;
	}
};

struct Edge
{
	int from, to;
	double dist;
};
vector <Edge> edges;
vector <int> G[maxn];
bool done[maxn];
double d[maxn];
int n, m, t;

void AddEdge(int from, int to, double dist)
{
	edges.push_back((Edge){from, to, dist});
	edges.push_back((Edge){to, from, dist});
	m = edges.size();
	G[from].push_back(m-2);
	G[to].push_back(m-1);
}

void Dijkstra()
{
	priority_queue <HeapNode> Q;
	for(int i = 1; i <= n; i++)
		d[i] = INF;
	d[1] = 0;
	memset(done, 0, sizeof(done));
	Q.push((HeapNode){0, 1});
	while(!Q.empty())
	{
		HeapNode x = Q.top();Q.pop();
		int u = x.u;
		if(done[u])
			continue;
		done[u] = true;
		//printf("%d\n", u);
		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;
				Q.push((HeapNode){d[e.to], e.to});
			} 
		}
	}
}
int main()
{
	int cas = 1;
	while(scanf("%d %d", &n, &t) && (n+t))
	{
		edges.clear();
		for(int i = 1;i <= n; i++)
			G[i].clear();
		for(int i = 1; i <= t; i++)
		{
			int u, v;
			double w;
			scanf("%d %d %lf", &u, &v, &w);
			AddEdge(u, v, w);
		}
		
		Dijkstra();
		double ans = d[1];
		int p1 = 1, p2 = 0;
		int flag = 1;
		for(int i = 1; i <= n; i++)
		{
			if(ans < d[i])
			{
				ans = d[i];
				p1 = i;
			}
		}
		for(int i = 1; i <= n; i++)
		{
			for(int j = 0; j < G[i].size(); j++)
			{
				Edge e = edges[G[i][j]];
				double s = (d[i] + d[e.to] + e.dist) / 2;
				if(s > ans)
				{
					flag = 0;
					ans = s;
					if(i < e.to)
					{
						p1 = i;
						p2 = e.to;
					}
					else
					{
						p2 = i;
						p1 = e.to;
					}
				}
			}
		}
		if(flag)
		{
			printf("System #%d\nThe last domino falls after %.1f seconds, at key domino %d.\n\n", cas++, ans, p1);
		}
		else
		{
			printf("System #%d\nThe last domino falls after %.1f seconds, between key dominoes %d and %d.\n\n", cas++, ans, p1, p2);
		}
	}
	return 0;
}

TOJ 1883 ZOJ 1298 POJ 1135 Domino Effect / Dijkstra,布布扣,bubuko.com

TOJ 1883 ZOJ 1298 POJ 1135 Domino Effect / Dijkstra

原文：http://blog.csdn.net/u011686226/article/details/19973387