BZOJ [HAOI2007]理想的正方形

#include<iostream>
#include<cstdio>
#include<cstring>
using namespace std;
const int maxn=1009;
int n,m,k;
int ans=1000000000;
int a[maxn][maxn];

int mn[maxn][maxn];
int mx[maxn][maxn];

int tmp1[maxn][maxn];

int q[maxn],head,tail;

int main(){
    scanf("%d%d%d",&n,&m,&k);
    for(int i=1;i<=n;++i){
        for(int j=1;j<=m;++j){
            scanf("%d",&a[i][j]);
        }
    }
    
    for(int i=1;i<=n;++i){
        head=1;tail=0;
        for(int j=1;j<=m;++j){
            while((head<=tail)&&(j-q[head]+1>k))++head;
            while((head<=tail)&&(a[i][q[tail]]>=a[i][j]))--tail;
            q[++tail]=j;
            if(j>=k)tmp1[i][j-k+1]=a[i][q[head]];
        }
    }
    for(int j=1;j<=m;++j){
        head=1;tail=0;
        for(int i=1;i<=n;++i){
            while((head<=tail)&&(i-q[head]+1>k))++head;
            while((head<=tail)&&(tmp1[q[tail]][j]>=tmp1[i][j]))--tail;
            q[++tail]=i;
            if(i>=k)mn[i-k+1][j]=tmp1[q[head]][j];
        }
    }

    for(int i=1;i<=n;++i){
        head=1;tail=0;
        for(int j=1;j<=m;++j){
            while((head<=tail)&&(j-q[head]+1>k))++head;
            while((head<=tail)&&(a[i][q[tail]]<=a[i][j]))--tail;
            q[++tail]=j;
            if(j>=k)tmp1[i][j-k+1]=a[i][q[head]];
        }
    }
    for(int j=1;j<=m;++j){
        head=1;tail=0;
        for(int i=1;i<=n;++i){
            while((head<=tail)&&(i-q[head]+1>k))++head;
            while((head<=tail)&&(tmp1[q[tail]][j]<=tmp1[i][j]))--tail;
            q[++tail]=i;
            if(i>=k)mx[i-k+1][j]=tmp1[q[head]][j];
        }
    }
    
    for(int i=1;i<=n-k+1;++i){
        for(int j=1;j<=m-k+1;++j){
            ans=min(ans,mx[i][j]-mn[i][j]);
        }
    }
    cout<<ans<<endl;
    return 0;
}