POJ 1847 Tram （簡單最短路徑dijkstra-floyd-spfa）

題目鏈接：http://poj.org/problem?id=1847

大意：給你N個交叉路口，每個路口都對應幾個路口，第一個不用開關，其餘要扳動開關，S到T，問你需要扳動幾次開關

思路：把第一個賦值爲0，其餘爲1，進行最短路徑算法

上代碼

//VJ上測試的時間
//dijkstra 0ms
//spaf     0ms
//floyd    32ms
#include<iostream>
#include<cmath>
#include<cstring>
#include<algorithm>
#include<stack>
#include<queue>
#include<vector>
#include<cstdio>
#include<string>
#include<map>
using namespace std;
#define ll long long
#define inf 0x3f3f3f3f
#define Max 110
int n, d[Max], M[Max][Max];
bool visit[Max];
vector<pair<int, int> >G[Max];
void init()
{
	for (int i = 1; i <= n; i++)
	{
		visit[i] = false;
		d[i] = inf;
		for(int j=1;j<=n;j++)
		M[i][j]=inf;
	}
}
void dijkstra(int l, int r)
{
	priority_queue<pair<int, int> >PQ;
	d[l] = 0;
	PQ.push(make_pair(0, l));
	while (!PQ.empty())
	{
		pair<int, int>f = PQ.top();
		PQ.pop();
		int u = f.second;
		if (d[u]<f.first*(-1))
			continue;
		visit[u] = 1;
		for (int i = 0; i<G[u].size(); i++)
		{
			int v = G[u][i].first;
			if (visit[v] == 1)
				continue;
			if (d[v]>d[u] + G[u][i].second)
			{
				d[v] = d[u] + G[u][i].second;
				PQ.push(make_pair(d[v] * (-1), v));
			}
		}
	}
	if (d[r] == inf)
		cout << -1 << endl;
	else
		cout << d[r] << endl;
}
void spfa(int l, int r)
{
	queue<int> Q;
	Q.push(l);
	d[l] = 0;
	visit[l] = true;//與dijkstra的區別是spfa判斷的是節點l是不是在隊列裏面，而dijkstra判斷該點是不是最優點
	while (!Q.empty())
	{
		int u = Q.front();
		Q.pop();
		for (int i = 0; i<G[u].size(); i++)
		{
			int v = G[u][i].first;
			if (d[v]>d[u] + G[u][i].second)
			{
				d[v] = d[u] + G[u][i].second;
				if (visit[v] == false)
				{
					Q.push(v);
					visit[v] = true;
				}
			}
		}
		visit[u] = false;
	}
	if (d[r] == inf)
		printf("-1\n");
	else
		printf("%d\n", d[r]);
}
void floyd(int l, int r)
{
	for (int k = 1; k <= n; k++)
		for (int i = 1; i <= n; i++)
			for (int j = 1; j <= n; j++)
				M[i][j] = min(M[i][k] + M[k][j], M[i][j]);
	if (M[l][r] == inf)
		cout << -1 << endl;
	else
		cout << M[l][r] << endl;
}
int main()
{
	//freopen("Text.txt", "r", stdin);
	int start, end, num, a;
	while (scanf("%d%d%d", &n, &start, &end) != EOF)
	{
		//交點1~n
		init();
		for (int i = 1; i <= n; i++)
		{
			scanf("%d", &num);
			for (int j = 0; j<num; j++)
			{
				scanf("%d", &a);
				if (j == 0)
				{
					G[i].push_back(make_pair(a, 0));
					M[i][a]=0;
				}
				else
				{
					G[i].push_back(make_pair(a, 1));
					M[i][a]=1;
				}
			}
		}
		dijkstra(start, end);
		spfa(start,end);
		floyd(start,end);
		for (int i = 1; i <= n; i++)
			G[i].clear();
	}
	return 0;
}