1996: [Hnoi2010]chorus 合唱队

Description

Input

Output

Sample Input
4
1701 1702 1703 1704
Sample Output
8
HINT

水题，区间dp，f[l,r,k]表示区间[l,r]最后一个是左（k=0）还是右（k=1）的方案数

const
        maxn=1010;
        h=19650827;
var
        f:array[0..maxn,0..maxn,0..1]of longint;
        a:array[0..maxn]of longint;
        n:longint;
 
procedure init;
var
        i:longint;
begin
        read(n);
        for i:=1 to n do
          begin
            read(a[i]);
            f[i,i,0]:=1;
          end;
end;
 
procedure dp;
var
        i,j:longint;
begin
        for i:=1 to n-1 do
          for j:=1 to n-i do
            begin
              f[j,j+i,0]:=(longint(a[j]<a[j+1])*f[j+1,j+i,0]+longint(a[j]<a[j+i])*f[j+1,j+i,1])mod h;
              f[j,j+i,1]:=(longint(a[j+i]>a[j])*f[j,j+i-1,0]+longint(a[j+i]>a[j+i-1])*f[j,j+i-1,1])mod h;
            end;
        writeln((f[1,n,0]+f[1,n,1])mod h);
end;
 
begin
        init;
        dp;
end.