51 nod 1444 破坏道路（BFS+枚举）

题目：http://www.51nod.com/onlineJudge/questionCode.html#!problemId=1444
思路：先求出各点的最短路（n<=3000），然后枚举重叠部分，寻找最少路数
代码：

#include <bits/stdc++.h>using namespace std;const int N = 3005;typedef long long ll;int n,m;struct node{    int v,w;    node(int v=0,int w=0):v(v),w(w){}};vector<int> G[N];int vis[N],d[N][N];void bfs(){    for(int s = 1;s <= n;s++)    {        memset(vis,0,sizeof(vis));        queue<int> q;        q.push(s);        vis[s] = 1;        while(!q.empty())        {            int u = q.front();q.pop();            for(int i = 0;i < G[u].size();i++)            {                int v = G[u][i];                if(!vis[v])                {                    vis[v] = 1;                    d[s][v] = d[s][u]+1;                    q.push(v);                }            }        }    }}int main(){    scanf("%d%d",&n,&m);    int u,v;    for(int i = 0;i < m;i++)    {        scanf("%d%d",&u,&v);        G[u].push_back(v);        G[v].push_back(u);    }    int s1,t1,l1,s2,t2,l2;    scanf("%d%d%d%d%d%d",&s1,&t1,&l1,&s2,&t2,&l2);    bfs();    if(d[s1][t1] > l1 || d[s2][t2] > l2)        return 0 * printf("-1\n");    int minn = d[s1][t1]+d[s2][t2];    for(int i = 1;i <= n;i++)    {        for(int j = 1;j <= n;j++)        {            if(d[s1][i]+d[i][j]+d[j][t1] <= l1 && d[s2][i]+d[i][j]+d[j][t2] <= l2)                minn = min(minn, d[s1][i]+d[i][j]+d[j][t1]+d[s2][i]+d[j][t2]);            if(d[s1][i]+d[i][j]+d[j][t1] <= l1 && d[t2][i]+d[i][j]+d[j][s2] <= l2)                minn = min(minn, d[s1][i]+d[i][j]+d[j][t1]+d[t2][i]+d[j][s2]);        }    }    printf("%d\n",m-minn);}