不知道为什么错了，我连程序的每一步都运行过，甚至试过打印每一步的动规f和路径，完全没发现问题，到底是怎么了？

我的程序：

var i,j,k,l,o,p,n,t:integer;

tu:array[0..20,0..20]of integer;

f:array[0..20,0..20]of integer;

w:array[0..20,0..20,1..2]of integer;

function max(a,b:integer):integer;

begin

max:=a;

if(b>a)then max:=b;

end;

begin

readln(n);

for i:=1 to n do begin

for j:=1 to n do read(tu);

end;

p:=0;

for o:=1 to 3 do begin

for i:=1 to n do begin

f[i][i]:=max(f[i],f[i])+tu[i][i];

if(f[i]>f[i])then begin w[i][i][1]:=i-1; w[i][i][2]:=i; end

else begin w[i][i][1]:=i; w[i][i][2]:=i-1; end;

for j:=i+1 to n do begin

f[j][i]:=max(f[j-1][i],f[j])+tu[j][i];

f[i][j]:=max(f[j],f[i][j-1])+tu[i][j];

if(f[j-1][i]>f[j])then begin w[j][i][1]:=j-1; w[j][i][2]:=i; end

else begin w[j][i][1]:=j; w[j][i][2]:=i-1; end;

if(f[j]>f[i][j-1])then begin w[i][j][1]:=i-1; w[i][j][2]:=j; end

else begin w[i][j][1]:=i; w[i][j][2]:=j-1; end;

end;

end;

i:=n;

j:=n;

while (i0)or(j0) do begin

tu[i][j]:=0;

t:=i;

i:=w[i][j][1];

j:=w[t][j][2];

end;

p:=p+f[n][n];

end;

writeln(p);

end.

相当令人郁闷啊……