POJ1050

题意:最大子矩阵.

分析:枚举矩形的上下边界,将权值纵向累加到一列上,求最大连续子序列和.复杂度O(N^3).

code:

const oo=100000000;
var   a,sum:array[0..110,0..110] of longint;
      s:array[0..110] of longint;
      n,i,j,k:longint;
      ans,max,now,maxnow:longint;


      function maxx(a,b:longint):longint;
      begin
            if a>b then exit(a); exit(b);
      end;


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

      for i:=1 to n do
         for j:=1 to n do
         sum[i,j]:=sum[i-1,j]+a[i,j];

      max:=-oo;
      for i:=1 to n do
         for j:=i to n do
         begin
               fillchar(s,sizeof(s),0);
               for k:=1 to n do
               begin
                     now:=sum[j,k]-sum[i-1,k];
                     s[k]:=maxx(s[k-1]+now,now);
               end;

               maxnow:=-oo;
               for k:=1 to n do
               if s[k]>maxnow then maxnow:=s[k];
               if maxnow>max then max:=maxnow;
         end;
      writeln(max);
end.