1996: [Hnoi2010]chorus 合唱队 - BZOJ

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=;
         h=;
 var
         f:array[..maxn,..maxn,..]of longint;
         a:array[..maxn]of longint;
         n:longint;

 procedure init;
 var
         i:longint;
 begin
         read(n);
         for i:= to n do
           begin
             read(a[i]);
             f[i,i,]:=;
           end;
 end;

 procedure dp;
 var
         i,j:longint;
 begin
         for i:= to n- do
           for j:= to n-i do
             begin
               f[j,j+i,]:=(longint(a[j]<a[j+])*f[j+,j+i,]+longint(a[j]<a[j+i])*f[j+,j+i,])mod h;
               f[j,j+i,]:=(longint(a[j+i]>a[j])*f[j,j+i-,]+longint(a[j+i]>a[j+i-])*f[j,j+i-,])mod h;
             end;
         writeln((f[,n,]+f[,n,])mod h);
 end;

 begin
         init;
         dp;
 end.