bzoj 1996: [Hnoi2010]chorus 合唱队

 1 #include<cstdio>
 2 #include<iostream>
 3 #include<cstring>
 4 #include<cstdlib>
 5 #include<cmath>
 6 #include<queue>
 7 #include<algorithm>
 8 #include<vector>
 9 #define M 1009
10 #define EPS 1e-10
11 #define MO 19650827
12 #define ll long long
13 using namespace std;
14 ll read()
15 {
16     char ch=getchar();
17     ll x=0,f=1;
18     for(;ch<‘0‘||ch>‘9‘;ch=getchar())
19         if(ch==‘-‘)
20           f=-1;
21     for(;ch>=‘0‘&&ch<=‘9‘;ch=getchar())
22         x=x*10+ch-‘0‘;
23     return x*f;
24 }
25 int n,f[M][M][2],a[M];
26 void jia(int &x,int y)
27 {
28   x+=y;
29   if(x>MO)
30     x-=MO;
31 }
32 int main()
33 {
34    n=read();
35    for(int i=1;i<=n;i++)
36      a[i]=read();
37    for(int i=1;i<=n;i++)
38      f[i][i][0]=1;
39    for(int i=n;i;i--)
40      for(int j=i+1;j<=n;j++)
41        {
42          if(a[i+1]>a[i])
43            jia(f[i][j][0],f[i+1][j][0]);
44          if(a[j]>a[i])
45            jia(f[i][j][0],f[i+1][j][1]);
46          if(a[j-1]<a[j])
47            jia(f[i][j][1],f[i][j-1][1]);
48          if(a[i]<a[j])
49            jia(f[i][j][1],f[i][j-1][0]);
50        }
51    printf("%d\n",(f[1][n][0]+f[1][n][1])%MO);
52    return 0;
53 }