BZOJ 1934 [Shoi2007]Vote 善意的投票

 //Twenty
#include<cstdio>
#include<cstdlib>
#include<iostream>
#include<algorithm>
#include<cmath>
#include<cstring>
#include<queue>
#include<vector>
const int maxn=20050,maxm=200050,INF=0x7f7f7f7f;
using namespace std;
int n,m,s,t,u,v,w,ecnt=1,fir[maxn],d[maxn],cur[maxn],c[maxn],p[maxn];
struct edge {
    int from,to,cap,flow,nxt;
    edge(){}
    edge(int from,int to,int cap,int flow,int nxt):from(from),to(to),cap(cap),flow(flow),nxt(nxt){}
}e[maxm];
void add(int u,int v,int w) {
    e[++ecnt]=edge(u,v,w,0,fir[u]);     
    e[++ecnt]=edge(v,u,0,0,fir[v]); 
    fir[u]=ecnt-1; fir[v]=ecnt;
}
queue<int>que;
void bfs(int s,int t) {
    for(int i=1;i<=n;i++) d[i]=n;
    d[t]=0; 
    que.push(t);
    while(!que.empty()) {
        int x=que.front() ;que.pop();
        for(int i=fir[x];i;i=e[i].nxt) 
        if(d[e[i].to]==n&&e[i].flow==e[i].cap) {
            d[e[i].to]=d[x]+1;
            que.push(e[i].to); 
        }
    }
}
int cal(int s,int t) {
    int fl=INF;
    for(int x=t;x!=s;x=e[p[x]].from) 
        fl=min(fl,e[p[x]].cap-e[p[x]].flow);
    for(int x=t;x!=s;x=e[p[x]].from) {
        e[p[x]].flow+=fl;
        e[p[x]^1].flow-=fl;
    }
    return fl;
}
int maxflow(int s,int t) {
    bfs(s,t);
    int res=0;
    for(int i=1;i<=n;i++) cur[i]=fir[i],c[d[i]]++;
    for(int x=s;d[x]<n;) {
        if(x==t) {
            res+=cal(s,t);
            x=s;
        }
        int ok=0;
        for(int &i=cur[x];i;i=e[i].nxt) 
            if(d[e[i].to]+1==d[x]&&e[i].cap>e[i].flow){
                p[x=e[i].to]=i;
                ok=1; break;
            }
        if(!ok) {
            cur[x]=fir[x]; int M=n;
            for(int i=cur[x];i;i=e[i].nxt) 
                if(e[i].cap>e[i].flow)
                    M=min(M,d[e[i].to]+1);
            if(!(--c[d[x]])) break;
            c[d[x]=M]++;
            if(x!=s) x=e[p[x]].from;
        }
    }
    return res;
}
int main()
{
    scanf("%d%d",&n,&m);
    s=n+1; t=n+2;
    for(int i=1;i<=n;i++) {
        int x;
        scanf("%d",&x);
        if(x==1) add(s,i,1),add(i,t,0);
        else add(s,i,0),add(i,t,1);
    }
    n+=2;
    for(int i=1;i<=m;i++) {
        int x,y;
        scanf("%d%d",&x,&y);
        add(x,y,1);
        add(y,x,1);
    }
    printf("%d\n",maxflow(s,t));
    return 0;
}