不仅知道长度，还要知道子序列是什么

#include <iostream>

using namespace std;

const int N = 1010;

int n;
int a[N];
int f[N], g[N];

// g[N] 表示从谁转移过来的

int main()
{
    cin >> n;
    for (int i = 1; i <= n; i ++) cin >> a[i];

    for (int i = 1; i <= n; i ++)
    {
        f[i] = 1;
        g[i] = 0;
        for (int j = 1; j < i; j ++)
            if (a[i] > a[j])
                if (f[i] < f[j] + 1)
                    {
                        f[i] = f[j] + 1;
                        g[i] = j;
                    }
    }

    int k = 1;
    for (int i = 1; i <= n; i ++)
        if (f[i] > f[k]) k = i;
    cout << f[k] << endl;

    for (int i = 0, len = f[k]; i < len; i ++)
    {
        cout << a[k] << ' ';
        k = g[k];
    }
    return 0;
}