做了北大的题 == 我上了北大

#include <iostream>
using namespace std;

const int N = 1010;
int a[N], f[N], g[N], n, res;

int main()
{
    cin >> n;
    for ( int i = 1; i <= n; i ++ ) cin >> a[i];
    for ( int i = 1; i <= n; i ++ ) 
    {
        f[i] = 1;
        for ( int j = 1; j < i; j ++ )
            if ( a[i] > a[j] ) f[i] = max(f[i], f[j] + 1);
    }
    for ( int i = n; i; i -- )
    {
        g[i] = 1;
        for ( int j = n; j > i; j -- )
            if ( a[i] > a[j] ) g[i] = max(g[i], g[j] + 1);
    }
    for ( int i = 1; i <= n; i ++ ) res = max(res, f[i] + g[i] - 1);
    cout << res << endl;
    return 0;
}