bzoj1532 [POI2005]Kos-Dicing（二分+最大流）

二分答案，最大流判是否满流。

#include <cstdio>#include <cstring>#include <algorithm>#include <queue>#include <cmath>using namespace std;#define ll long long#define inf 0x3f3f3f3f#define N 20010inline int read(){    int x=0,f=1;char ch=getchar();    while(ch<'0'||ch>'9'){if(ch=='-')f=-1;ch=getchar();}    while(ch>='0'&&ch<='9') x=x*10+ch-'0',ch=getchar();    return x*f;}int n,m,h[N],num=1,T=20001,lev[N],cur[N];struct edge{    int to,next,val;}data[90000];inline void add(int x,int y,int val){    data[++num].to=y;data[num].next=h[x];h[x]=num;data[num].val=val;    data[++num].to=x;data[num].next=h[y];h[y]=num;data[num].val=0;}inline bool bfs(){    queue<int>q;memset(lev,0,sizeof(lev));    lev[0]=1;q.push(0);    while(!q.empty()){        int x=q.front();q.pop();        for(int i=h[x];i;i=data[i].next){            int y=data[i].to;if(lev[y]||!data[i].val) continue;            lev[y]=lev[x]+1;if(y==T) return 1;q.push(y);        }    }return 0;}inline int dinic(int x,int low){    if(x==T) return low;int tmp=low;    for(int &i=cur[x];i;i=data[i].next){        int y=data[i].to;if(lev[y]!=lev[x]+1||!data[i].val) continue;        int res=dinic(y,min(data[i].val,tmp));        if(!res) lev[y]=0;else data[i].val-=res,data[i^1].val+=res,tmp-=res;        if(!tmp) return low;    }return low-tmp;}inline bool jud(int x){    num=1;int ans=0;    for(int i=1;i<=n;++i) data[++num].val=x,data[++num].val=0;    for(int i=1;i<=m*3;++i) data[++num].val=1,data[++num].val=0;    while(bfs()){memcpy(cur,h,sizeof(cur));ans+=dinic(0,inf);}    return ans==m;}int main(){//  freopen("a.in","r",stdin);    n=read();m=read();    for(int i=1;i<=n;++i) add(i,T,0);    for(int i=1;i<=m;++i){        add(n+i,read(),1);add(n+i,read(),1);add(0,n+i,1);    }int l=1,r=m;    while(l<=r){        int mid=l+r>>1;        if(jud(mid)) r=mid-1;        else l=mid+1;    }printf("%d\n",r+1);    return 0;}