PAT A 1018. Public Bike Management (30)【最短路径】

#include<cstdio>
#include<string>
#include<cstring>
#include<vector>
#include<iostream>
#include<queue>
#include<algorithm>
using namespace std;
typedef long long LL;
const int INF = 0x7FFFFFFF;
const int maxn = 1e3 + 10;
int c, n, s, m, f[maxn], map[maxn][maxn], x, y, z, dis[maxn], vis[maxn], ans;

void dfs(int x, int y)
{
	if (y < 0) return;
	if (x == s) { ans = min(ans, y); return; }
	for (int i = 0; i <= n; i++)
	{
		if (map[x][i] == -1) continue;
		if (dis[i] == dis[x] + map[x][i]) dfs(i, y - (c / 2 - f[i]));
	}
}

bool Dfs(int x, int y, int z)
{
	if (!x) { if (y == z) { printf("0"); return true; } else return false; }
	for (int i = 0; i <= n; i++)
	{
		if (map[x][i] == -1) continue;
		if (dis[x] == dis[i] + map[x][i])
		{
			if (Dfs(i, y + c / 2 - f[x], z))
			{
				printf("->%d", x);
				return true;
			}
		}
	}
	return false;
}

int main()
{
	scanf("%d%d%d%d", &c, &n, &s, &m);
	for (int i = 1; i <= n; i++) scanf("%d", &f[i]);
	memset(map, -1, sizeof(map));
	memset(dis, -1, sizeof(dis));
	while (m--)
	{ 
		scanf("%d%d%d", &x, &y, &z);
		if (map[x][y] == -1 || map[x][y] > z) map[x][y] = map[y][x] = z;
	}
	dis[0] = 0;
	while (true)
	{
		int now = -1;
		for (int i = 0; i <= n; i++)
		{
			if (!vis[i] && dis[i] != -1 && (now == -1 || dis[i] < dis[now])) now = i;
		}
		if (now == -1) break;
		vis[now] = 1;
		for (int i = 0; i <= n; i++)
		{
			if (map[now][i] == -1) continue;
			if (dis[i] == -1 || dis[i]>dis[now] + map[now][i]) dis[i] = dis[now] + map[now][i];
		}
	}
	int q = 0, h = n*c / 2;
	while (q <= h)
	{
		int mid = q + h >> 1;
		ans = INF;	dfs(0, mid);
		if (ans != INF) h = mid - 1; else q = mid + 1;
	}
	printf("%d ", q);//需要运出的数量
	dfs(0, q);
	Dfs(s, ans, q);
	printf(" %d
", ans);//需要运回的数量
	return 0;
}