【最短路】 Codeforces Round #302 (Div. 1) B - Destroying Roads

先对所有点做bfs求出任意两点间最短距离，然后暴力枚举中转点i，j求出答案。。。。

#include <iostream>
#include <queue>
#include <stack>
#include <map>
#include <set>
#include <bitset>
#include <cstdio>
#include <algorithm>
#include <cstring>
#include <climits>
#include <cstdlib>
#include <cmath>
#include <time.h>
#define maxn 3005
#define maxm 10005
#define eps 1e-12
#define mod 998244353
#define INF 0x3f3f3f3f
#define PI (acos(-1.0))
#define lowbit(x) (x&(-x))
#define mp make_pair
#define ls o<<1
#define rs o<<1 | 1
#define lson o<<1, L, mid 
#define rson o<<1 | 1, mid+1, R
#pragma comment(linker, "/STACK:102400000,102400000")
#define pii pair<int, int> 
typedef long long LL;
typedef unsigned long long ULL;
//typedef int LL;
using namespace std;
LL qpow(LL a, LL b){LL res=1,base=a;while(b){if(b%2)res=res*base;base=base*base;b/=2;}return res;}
LL powmod(LL a, LL b){LL res=1,base=a;while(b){if(b%2)res=res*base%mod;base=base*base%mod;b/=2;}return res;}
// head

struct Edge
{
	int v;
	Edge *next;
}*H[maxn], E[maxm], *edges;

queue<pii> q;
int dis[maxn][maxn];
int n, m, ans;

void addedges(int u, int v)
{
	edges->v = v;
	edges->next = H[u];
	H[u] = edges++;
}

void init()
{
	edges = E;
	memset(H, 0, sizeof H);
	memset(dis, INF, sizeof dis);
}

void bfs(int now)
{
	q.push(mp(now, 0));
	while(!q.empty()) {
		int u = q.front().first, dist = q.front().second;
		q.pop();
		if(dis[now][u] != INF) continue;
		dis[now][u] = dist;
		for(Edge *e =  H[u]; e; e = e->next) {
			int v = e->v;
			if(dist + 1 < dis[now][v])
				q.push(mp(v, dist + 1));
		}
	}
}

void calc(int s0, int t0, int l0, int s1, int t1, int l1)
{
	for(int i = 1; i <= n; i++)
		for(int j = 1; j <= n; j++)
			if(dis[s0][i] + dis[i][j] + dis[j][t0] <= l0)
				if(dis[s1][i] + dis[i][j] + dis[j][t1] <= l1)
					ans = min(ans, dis[s0][i] + dis[j][t0] + dis[s1][i] + dis[j][t1] + dis[i][j]);
}

void work()
{
	int u, v, cnt = 0;
	for(int i = 1; i <= m; i++) {
		scanf("%d%d", &u, &v);
		addedges(u, v);
		addedges(v, u);
		cnt++;
	}
	
	for(int i = 1; i <= n; i++) bfs(i);
	int s0, t0, l0, s1, t1, l1;
	scanf("%d%d%d", &s0, &t0, &l0);
	scanf("%d%d%d", &s1, &t1, &l1);
	ans = INF;
	if(dis[s0][t0] <= l0 && dis[s1][t1] <= l1) ans = dis[s0][t0] + dis[s1][t1];
	else {
		printf("-1\n");
		return;
	}
	calc(s0, t0, l0, s1, t1, l1);
	calc(t0, s0, l0, s1, t1, l1);
	printf("%d\n", cnt - ans);
}

int main()
{
	while(scanf("%d%d", &n, &m)!=EOF) {
		init();
		work();
	}	
	
	
	return 0;
}