UVa 10534 Wavio Sequence

#include <bits/stdc++.h> 
using namespace std;
const int N=10000+10;
int a[N],dp[N], lis[N],lds[N];
int main()
{
    int n;
    while (scanf("%d", &n) != EOF){
        for (int i=0;i<n;i++) scanf("%d",&a[i]);
         memset(dp,0,sizeof(dp));
        int pos=0;   
        dp[0]=a[0];lis[0]=0;
        for(int i=1; i<n; i++)
        {
            if(a[i]>dp[pos]) 
                dp[++pos] = a[i];
            else  
                dp[lower_bound(dp,dp+pos+1,a[i])-dp]=a[i];  
            lis[i]=pos;
        }
        memset(dp,0,sizeof(dp));
        pos=0;   
        dp[0]=a[n-1];lds[n-1]=0;
        for(int i=n-1; i>=0; i--)
        {
            if(a[i]>dp[pos]) 
                dp[++pos] = a[i];
            else  
                dp[lower_bound(dp,dp+pos+1,a[i])-dp]=a[i];  
            lds[i]=pos;
        }
        int ans=0;
        for (int i=0;i<n;i++)
            ans=max(ans,min(lis[i],lds[i]));
        printf("%d\n",ans*2+1);
    }
    
    return 0;
}