Recently, I have tried a problem: 1893B - Neutral Tonality and solved it with O(NlogN) tc.

Problem Summary: Insert array b into array a at any position while making sure that the LIS is minized.

Approach: For an element el of the array a insert the elements of b which are greater than or equal to el.

However, the solution got TLE on the third test case: Submission 282567664

What's wrong in my approach/code? Can anyone help me to debug this problem?

Code: Used multiset to find elements and map to store the elements.

void solve()
{
    int n, m, x;
    cin >> n >> m;

    vi a(n);
    multiset<int> ms;
    for (int i = 0; i < n; i++)
        cin >> a[i];
    for (int i = 0; i < m; i++)
        cin >> x, ms.insert(x);

    map<int, vi> elements;
    forr(i, 0, n - 1)
    {
        auto it = lb(a[i], ms);
        while (it != ms.end())
        {
            elements[i].pb(*it);
            ms.erase(it);
            if (!sz(ms))
                break;
            it = lb(a[i], ms);
        }
    }

    forr(i, 0, n - 1)
    {
        reverse(all(elements[i]));
        for (int v : elements[i])
            printsp(v);
        printsp(a[i]);
    }

    while (sz(ms))
        printsp(*ms.rbegin()), ms.erase(--ms.end());
}