Codeforces 509F Progress Monitoring

 1 #include<cstdio>
 2 #include<cmath>
 3 #include<algorithm>
 4 #include<cstring>
 5 #include<iostream>
 6 #define ll long long
 7 const ll Mod=1000000007;
 8 int a[200005];
 9 ll f[5005][5005];
10 int read(){
11     int t=0,f=1;char ch=getchar();
12     while (ch<‘0‘||ch>‘9‘){if (ch==‘-‘) f=-1;ch=getchar();}
13     while (‘0‘<=ch&&ch<=‘9‘){t=t*10+ch-‘0‘;ch=getchar();}
14     return t*f;
15 }
16 ll dfs(int l,int r){
17     if (l>=r){
18         return (f[l][r]=1);
19     }
20     if (f[l][r]!=-1){
21         return f[l][r];
22     }
23     ll res=0;
24     for (int i=l+1;i<=r;i++)
25       if (i==r||a[l+1]<a[i+1])
26     {
27         res=(res+((dfs(l+1,i)*dfs(i,r)))%Mod)%Mod;
28     }
29     return f[l][r]=res;
30 }
31 int main(){
32     int n=read();
33     for (int i=1;i<=n;i++)
34      for (int j=1;j<=n;j++)
35       f[i][j]=-1;
36     for (int i=1;i<=n;i++) a[i]=read();
37     printf("%I64d\n",dfs(1,n));
38     return 0;
39 }