bzoj1163 [Baltic2008]Mafia

#include<queue>
#include<cstdio>
#include<cstring>
#include<algorithm>
#define M 110000
#define inf 0x3f3f3f3f
#define N 440
using namespace std;
inline char gc(){
    static char now[1<<16],*S,*T;
    if (T==S){T=(S=now)+fread(now,1,1<<16,stdin);if (T==S) return EOF;}
    return *S++;
}
inline int read(){
    int x=0;char ch=gc();
    while(ch<'0'||ch>'9') ch=gc();
    while(ch<='9'&&ch>='0') x=x*10+ch-'0',ch=gc();return x;
}
struct node{
    int y,z,next;
}data[200000];
int h[N],cur[N],level[N],n,m,s,t,T,num=1;
inline void insert1(int x,int y,int z){
    data[++num].y=y;data[num].z=z;data[num].next=h[x];h[x]=num;
    data[++num].y=x;data[num].z=0;data[num].next=h[y];h[y]=num;
}
inline bool bfs(){
    memset(level,0,sizeof(level));level[s]=1;queue<int>q;q.push(s);
    while(!q.empty()){
        int x=q.front();q.pop();
        for (int i=h[x];i;i=data[i].next){
            int y=data[i].y,z=data[i].z;
            if(level[y]||!z) continue;q.push(y);level[y]=level[x]+1;if (y==T) return 1;
        }
    }return 0;
}
inline int dfs(int x,int s){
    if (x==T) return s;int ss=s;
    for (int &i=cur[x];i;i=data[i].next){
        int y=data[i].y,z=data[i].z;
        if (level[x]+1==level[y]&&z){
            int xx=dfs(y,min(z,s));if (!xx) level[y]=0;
            s-=xx;data[i].z-=xx;data[i^1].z+=xx;if (!s) return ss;
        }
    }return ss-s;
}
int main(){
    //freopen("bzoj1163.in","r",stdin);
    n=read();m=read();
    s=read();t=read();
    for (int i=1;i<=n;++i) insert1(i,i+n,read());
    for (int i=1;i<=m;++i){
        int x=read(),y=read();insert1(x+n,y,inf);insert1(y+n,x,inf);
    }T=n+t;int ans=0;
    while(bfs()) memcpy(cur,h,sizeof(cur)),ans+=dfs(s,inf);printf("%d",ans);
    return 0;
}