[WF2011] Chips Challenge

Solution

Coding

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#include<queue>
#define ll long long
using namespace std;
const int N=1e3+10;
const int M=1e4+100;
const int inf=1e9;
const int maxn=1e4;
int n,A,B,tot,s,t,maxflow,flow,sum,cnt,a[50][50],ver[M],Next[M],edge[M],lin[N],d[N],incf[N],pre[N],cost[M],v[N];
char ch[50];
void add(int x,int y,int z,int val){
	ver[++tot]=y;Next[tot]=lin[x];lin[x]=tot;edge[tot]=z;cost[tot]=val;
	ver[++tot]=x;Next[tot]=lin[y];lin[y]=tot;edge[tot]=0;cost[tot]=-val;
}
bool spfa(){
	queue<int>q;
	memset(d,0xcf,sizeof(d));
	memset(v,0,sizeof(v));
	q.push(s),v[s]=1,d[s]=0;
	incf[s]=1e9;
	while(q.size()){
		int x=q.front();q.pop();v[x]=0;
		for(int i=lin[x];i;i=Next[i]){
			if(edge[i]){
				int y=ver[i];
				if(d[y]<d[x]+cost[i]){
					d[y]=d[x]+cost[i];
					if(!v[y]) v[y]=1,q.push(y);
					incf[y]=min(incf[x],edge[i]);
					pre[y]=i;
				}
			}
		}
	}
	if(d[t]==0xcfcfcfcf) return 0;
	return 1;
}
void update(){
	int x=t;
	while(x!=s){
		int i=pre[x];
		edge[i]-=incf[t];
		edge[i^1]+=incf[t];
		x=ver[i^1];
	}
	sum+=incf[t]*d[t];
}
int main(){
	//freopen("1.in","r",stdin);
	//freopen("1.out","w",stdout);
	while(scanf("%d%d%d",&n,&A,&B)){
		if(n==0&&A==0&&B==0) break;
		s=0,t=2*n+1;cnt++;
		memset(a,-1,sizeof(a));
		int dd=0;
		for(int i=1;i<=n;++i){
			scanf("%s",ch+1);
			for(int j=1;j<=n;++j){
				if(ch[j]=='C') a[i][j]=1,dd++;
				else if(ch[j]=='/') a[i][j]=0;
			}
		}
		int ans;
		for(ans=n*n;ans>0;--ans){
			memset(lin,0,sizeof(lin));
			tot=1;int num=ans*A/B;int temp=0;
			for(int i=1;i<=n;++i){
				for(int j=1;j<=n;++j){
					if(a[i][j]==-1) add(i,n+j,1,1);
					else if(a[i][j]==1) add(i,n+j,1,1+maxn),temp++; 
				}
				add(i,i+n,inf,0);add(s,i,num,0);add(i+n,t,num,0);
			}
			maxflow=flow=0;sum=0;
			while(spfa()) 
				update();
			sum-=temp*maxn;
			if(sum==ans){
				printf("Case %d: %d\n",cnt,ans-temp);break;
			}else ans=sum+1; 
		}
		if(ans<=0&&dd>0) printf("Case %d: impossible\n",cnt);
		else if(ans==0) printf("Case %d: 0\n",cnt);
	}
	return 0;
}