SPFA(建图) HDOJ 4725 The Shortest Path in Nya Graph

 

题目传送门

题意:有两种路径,每个点会分别在某一层,层相邻之间权值c.还有直接两点传送,花费w.问1到n的最短距离.

分析:1~n正常建边.然后n + a[i]表示i点在第a[i]层.然后再优化些就不会超时了.

 

#include <cstdio>
#include <algorithm>
#include <cstring>
#include <queue>
using namespace std;

const int N = 2e5 + 5;
const int E = N * 20;
const int INF = 0x3f3f3f3f;
struct Edge	{
	int v, w, nex;
	Edge() {}
	Edge(int v, int w, int nex) : v (v), w (w), nex (nex) {}
}edge[E];
int head[N];
int d[N];
int a[N];
bool vv[N];
bool vis[N];
int n, m, e;

void init(void)	{
	memset (head, -1, sizeof (head));
	memset (vv, false, sizeof (vv));
	e = 0;
}

void add_edge(int u, int v, int w)	{
	edge[e] = Edge (v, w, head[u]);
	head[u] = e++;
}

void SPFA(int s)	{
	memset (vis, false, sizeof (vis));
	memset (d, INF, sizeof (d));
	d[s] = 0;	vis[s] = true;
	queue<int> que;	que.push (s);
	while (!que.empty ())	{
		int u = que.front ();	que.pop ();
		vis[u] = false;
		for (int i=head[u]; ~i; i=edge[i].nex)	{
			int v = edge[i].v, w = edge[i].w;
			if (d[v] > d[u] + w)	{
				d[v] = d[u] + w;
				if (!vis[v])	{
					vis[v] = true;	que.push (v);
				}
			}
		}
	}
}

int main(void)	{
	int T, cas = 0;	scanf ("%d", &T);
	while (T--)	{
		init ();
		int c;	scanf ("%d%d%d", &n, &m, &c);
		for (int i=1; i<=n; ++i)	{
			scanf ("%d", &a[i]);
			vv[a[i]] = true;
		}
		for (int i=1; i<n; ++i)	{
			if (vv[i] && vv[i+1])	{
				add_edge (n+i, n+i+1, c);
				add_edge (n+i+1, n+i, c);
			}
		}
		for (int i=1; i<=n; ++i)	{
			add_edge (n+a[i], i, 0);
			if (a[i] > 1)	add_edge (i, n+a[i]-1, c);
			if (a[i] < n)	add_edge (i, n+a[i]+1, c);
		}
		for (int u, v, w, i=1; i<=m; ++i)	{
			scanf ("%d%d%d", &u, &v, &w);
			add_edge (u, v, w);	add_edge (v, u, w);
		}
		SPFA (1);
		printf ("Case #%d: %d\n", ++cas, d[n] == INF ? -1 : d[n]);
	}

	return 0;
}