【2020牛客暑期多校训练营（第二场）】F. Fake Maxpooling

知识点：单调队列

#include <cstdio>
#include <cstring>
using namespace std;
int n,m,k,head,tail;
int a[5010][5010];
int que[5010];
int p[5010][5010]={0},h2,t2,qq[5010];
long long ans=0;
int gcd(int x,int y)
{
    return y==0?x:gcd(y,x%y);
}
int main()
{
    scanf("%d %d %d",&n,&m,&k);
    for (int i=1;i<=n;i++)
        for (int j=1;j<=m;j++)
            a[i][j]=i/gcd(i,j)*j;
    for (int j=1;j<=m;j++)
    {
        for (int i=1;i<=n;i++) qq[i]=0;
        h2=t2=1;
        for (int i=1;i<k;i++)
        {
            while (t2>=h2 && a[i][j]>a[qq[t2]][j]) t2--;
            t2++;
            qq[t2]=i;
        }
        for (int i=k;i<=n;i++)
        {
            while (t2>=h2 && i-qq[h2]>=k) h2++;
            while (t2>=h2 && a[i][j]>a[qq[t2]][j]) t2--;
            t2++;
            qq[t2]=i;
            p[i-k+1][j]=a[qq[h2]][j];
        }
    }

    for (int i=1;i<=n-k+1;i++)
    {
        for (int j=1;j<=m;j++) que[j]=0;
        head=tail=1;
        for (int j=1;j<k;j++)
        {
            while (tail>=head && p[i][j]>p[i][que[tail]]) tail--;
            tail++;
            que[tail]=j;
        }
        for (int j=k;j<=m;j++)
        {
            while (tail>=head && j-que[head]>=k) head++;
            while (tail>=head && p[i][j]>p[i][que[tail]]) tail--;
            tail++;
            que[tail]=j;
            ans+=p[i][que[head]];
        }
    }
    printf("%lld\n",ans);
    return 0;
}