[luoguP3110] [USACO14DEC]驮运Piggy Back（SPFA || BFS）

传送门

以 1，2，n 为起点跑3次 bfs 或者 spfa

那么 ans = min(ans, dis[1][i] * B + dis[2][i] * E + dis[3][i] * P) (1 <= i <= n)

#include <queue>
#include <cstdio>
#include <cstring>
#include <iostream>
#define N 40001
#define LL long long
#define min(x, y) ((x) < (y) ? (x) : (y))

int B, E, P, n, m, cnt;
int dis[4][N], head[N], to[N << 1], next[N << 1];
bool vis[N];
std::queue <int> q;
LL ans = ~(1 << 31);

inline int read()
{
	int x = 0, f = 1;
	char ch = getchar();
	for(; !isdigit(ch); ch = getchar()) if(ch == '-') f = -1;
	for(; isdigit(ch); ch = getchar()) x = (x << 1) + (x << 3) + ch - '0';
	return x * f;
}

inline void add(int x, int y)
{
	to[cnt] = y;
	next[cnt] = head[x];
	head[x] = cnt++;
}

inline void spfa(int s, int k)
{
	int i, v, u;
	memset(vis, 0, sizeof(vis));
	memset(dis[k], 127, sizeof(dis[k]));
	q.push(s);
	dis[k][s] = 0;
	while(!q.empty())
	{
		u = q.front();
		q.pop();
		vis[u] = 0;
		for(i = head[u]; i ^ -1; i = next[i])
		{
			v = to[i];
			if(dis[k][v] > dis[k][u] + 1)
			{
				dis[k][v] = dis[k][u] + 1;
				if(!vis[v])
				{
					q.push(v);
					vis[v] = 1;
				}
			}
		}
	}
}

int main()
{
	int i, x, y;
	B = read();
	E = read();
	P = read();
	n = read();
	m = read();
	memset(head, -1, sizeof(head));
	for(i = 1; i <= m; i++)
	{
		x = read();
		y = read();
		add(x, y);
		add(y, x);
	}
	spfa(1, 1);
	spfa(2, 2);
	spfa(n, 3);
	for(i = 1; i <= n; i++)
		ans = min(ans, (LL)(dis[1][i] * B + dis[2][i] * E + dis[3][i] * P));
	printf("%lld
", ans);
	return 0;
}