【Luogu】P2219修筑绿化带（单调队列）

　　题目链接

　　这题各种边界判断恶心死人

　　就是单调队列在每行求出最小的、能装进A*B方块里的花坛

　　然后再在刚刚求出的那个东西里面跑一遍竖着的单调队列

　　然后……边界调了一小时

　　做完这题我深刻地感觉到我又强了

#include<cstdio>
#include<cstring>
#include<cstdlib>
#include<algorithm>
#include<cctype>
#include<queue>
#include<vector>
#define maxm 2000020
#define maxn 1010000
using namespace std;
inline long long read(){
    long long num=,f=;
    char ch=getchar();
    while(!isdigit(ch)){
        if(ch=='-')    f=-;
        ch=getchar();
    }
    while(isdigit(ch)){
        num=num*+ch-'';
        ch=getchar();
    }
    return num*f;
}

inline int count(int i){    return i&?i+:i-;    }

struct Edge{
    int next,to,val;
}edge[maxm*];
int head[maxn],num;
inline void addedge(int from,int to,int val){
    edge[++num]=(Edge){head[from],to,val};
    head[from]=num;
}
inline void add(int from,int to,int val){
    addedge(from,to,val);
    addedge(to,from,);
}

int dfn[maxn];
bool vis[maxn];
int Start,End;
int last[maxm],tot;

bool bfs(){
    for(register int i=;i<=tot;++i)    vis[last[i]]=;    tot=;
    dfn[Start]=;    vis[Start]=;
    queue<int>q;    q.push(Start);
    while(!q.empty()){
        int from=q.front();    q.pop();
        last[++tot]=from;
        for(int i=head[from];i;i=edge[i].next){
            int to=edge[i].to;
            if(vis[to]||edge[i].val==)    continue;
            dfn[to]=dfn[from]+;
            vis[to]=;    q.push(to);
        }
    }
    return vis[End];
}

int dfs(int x,int val,int limit){
    if(x<=&&x>limit)    return ;
    if(val==||x==End)    return val;
    int flow=;    vis[x]=;
    last[++tot]=x;
    for(int i=head[x];i;i=edge[i].next){
        int to=edge[i].to;
        if(edge[i].val==||vis[to]||dfn[to]!=dfn[x]+)    continue;
        int now=dfs(to,min(val,edge[i].val),limit);
        edge[i].val-=now;    edge[count(i)].val+=now;    val-=now;    flow+=now;
        if(val<=)    break;
    }
    if(flow!=val)    dfn[x]=-;
    return flow;
}

int maxflow(int limit){
    int ans=;
    while(bfs()){
        for(register int i=;i<=tot;++i)    vis[last[i]]=;    tot=;
        int now=dfs(Start,0x7fffffff,limit);
        if(!now)    break;
        return now;
    }
    return ans;
}

int main(){
    int n=read();
    End=n++;
    for(int i=;i<=n;++i){
        int a=read(),b=read();
        add(a,i+,);
        add(b,i+,);
        add(i+,End,);
    }
    int ans;
    for(ans=;;++ans){
        add(Start,ans,);
        if(maxflow(ans)==)    break;
    }
    printf("%d",ans-);
    return ;
}