【HAOI 2007】理想正方形

　　昨晚眼看宿舍就要熄灯锁门了，赶紧赶紧，终于把这个程序搞出来了……

　　就是单调队列。先按行维护每行每段的最大值(max[][])和最小值(min[][])，然后再按列将处理好的max[][]和min[][]维护最大值(ans_max[][])和最小值(ans_min[][])，最后枚举一下正方形的左上方坐标更新就ok了……

　　挺绕口的……看程序吧

var q:array[0..10000]of longint;
    max,min,ans_max,ans_min,w:Array[1..1000,1..1000]of longint;
    n,m,k,i,j,head,tail,ans:longint;

function cmp(a,b:longint):longint;
begin
     if a<b then cmp:=a
        else cmp:=b;
end;

begin
     readln(n,m,k);
     for i:=1 to n do
         for j:=1 to m do read(w[i,j]);

     for i:=1 to n do
         begin
              fillchar(q,sizeof(q),0);
              head:=1;tail:=0;
              for j:=1 to k-1 do
                  begin
                       while (head<=tail)and(w[i,q[tail]]<w[i,j]) do dec(tail);
                       inc(tail);q[tail]:=j;
                  end;
              for j:=k to m do
                  begin
                       while (head<=tail)and(w[i,q[tail]]<w[i,j]) do dec(tail);
                       inc(tail);q[tail]:=j;
                       while q[head]<j-k+1 do inc(head);
                       max[i,j-k+1]:=w[i,q[head]];
                  end;
         end;

     for i:=1 to n do
         begin
              fillchar(q,sizeof(q),0);
              head:=1;tail:=0;
              for j:=1 to k-1 do
                  begin
                       while (head<=tail)and(w[i,q[tail]]>w[i,j]) do dec(tail);
                       inc(tail);q[tail]:=j;
                  end;
              for j:=k to m do
                  begin
                       while (head<=tail)and(w[i,q[tail]]>w[i,j]) do dec(tail);
                       inc(tail);q[tail]:=j;
                       while q[head]<j-k+1 do inc(head);
                       min[i,j-k+1]:=w[i,q[head]];
                  end;
         end;

     for j:=1 to m-k+1 do
         begin
              fillchar(q,sizeof(q),0);
              head:=1;tail:=0;
              for i:=1 to k-1 do
                  begin
                       while (head<=tail)and(max[i,j]>max[q[tail],j]) do dec(tail);
                       inc(tail);q[tail]:=i;
                  end;
              for i:=k to n do
                  begin
                       while (head<=tail)and(max[i,j]>max[q[tail],j]) do dec(tail);
                       inc(tail);q[tail]:=i;
                       while q[head]<i-k+1 do inc(head);
                       ans_max[i-k+1,j]:=max[q[head],j];
                  end;

              fillchar(q,sizeof(q),0);
              head:=1;tail:=0;
              for i:=1 to k-1 do
                  begin
                       while (head<=tail)and(min[i,j]<min[q[tail],j]) do dec(tail);
                       inc(tail);q[tail]:=i;
                  end;
              for i:=k to n do
                  begin
                       while (head<=tail)and(min[i,j]<min[q[tail],j]) do dec(tail);
                       inc(tail);q[tail]:=i;
                       while q[head]<i-k+1 do inc(head);
                       ans_min[i-k+1,j]:=min[q[head],j];
                  end;
         end;

     ans:=maxlongint;
     for i:=1 to n-k+1 do
         for j:=1 to m-k+1 do
             ans:=cmp(ans,ans_max[i,j]-ans_min[i,j]);
     writeln(ans);
end.