BZOJ 1340. [Baltic2007]Escape逃跑问题


http://www.lydsy.com/JudgeOnline/problem.php?id=1340


const int N = 1009, M = int(4e6) + 9;

//struct Network_Flow{

int D[N], hd[N], suc[M], to[M], cap[M];
int n, m, s, t;

inline void ae(int x, int y, int c){
    suc[m] = hd[x], hd[x] = m, to[m] = y, cap[m++] = c,
    suc[m] = hd[y], hd[y] = m, to[m] = x, cap[m++] = 0;
}

inline void aee(int x, int y, int c){
    suc[m] = hd[x], hd[x] = m, to[m] = y, cap[m++] = c,
    suc[m] = hd[y], hd[y] = m, to[m] = x, cap[m++] = c;
}

#define v to[i]
#define c cap[i]
#define f cap[i^1]

LL sap(){
    LL z=0; static int cnt[N],cur[N],pre[N];
    fill(D,D+n,n),fill(cnt,cnt+n,0);cnt[n]=n;
    int u=s;cur[s]=hd[s];while (D[s]){
#define i cur[u]
        if (u==t){
            int d=INF;for(u=s;u!=t;u=v)checkMin(d,c);
            z+=d;for(u=s;u!=t;u=v)f+=d,c-=d;u=s;
        }
#undef i
        int i;for(i=cur[u];i;i=suc[i]){
            if(D[u]+1==D[v]&&c){cur[u]=i,cur[v]=hd[v],pre[v]=u,u=v;break;}
        }
        if (!i){
            if (!--cnt[D[u]])break;
            D[u]=1;REP_G(i,u)if(c)checkMax(D[u],D[v]);--D[u];
            ++cnt[D[u]];if(u==s)cur[u]=hd[u];else u=pre[u];
        }
    }

    return z;
}
#undef f
#undef c
#undef v
//} G;

int L, W;
int xx[N], yy[N];

void init(){

    RD(L, W); RD(n);
    REP_1(i, n) RD(xx[i], yy[i]);

    s = 0, t = 2*n + 1, m = 2;

    REP_1(i, n){
        ae(2*i-1,2*i,1);
        if (yy[i] <= 100) ae(s, 2*i-1, INF);
        if (yy[i] >= W - 100) ae(2*i, t, INF);
        FOR_1(j, i+1, n) if (sqr(xx[i]-xx[j]) + sqr(yy[i]-yy[j]) <= sqr(200)){
            ae(2*i, 2*j-1, INF);
            ae(2*j, 2*i-1, INF);
        }
    }

    n = t + 1;
}

int main(){

#ifndef ONLINE_JUDGE
    freopen("in.txt", "r", stdin);

#endif

    init(); OT(sap());
}