void del(node *peak)
{
    if (peak->l == NULL && peak->r == NULL)
    {
        if (peak->prev != NULL && peak->prev->key > peak->key)
        {
            peak->prev->l = NULL;
        } else if (peak->prev != NULL && peak->prev->key < peak->key)
        {
            peak->prev->r = NULL;
        }
        free(peak);
        peak = NULL;
        return;
    }
    if (peak->r == NULL)
    {
        if (peak->prev != NULL && peak->prev->key > peak->key)
        {
            peak->prev->l = peak->l;
        } else if (peak->prev != NULL && peak->prev->key < peak->key)
        {
            peak->prev->r = peak->l;
        }
        free(peak);
        return;
    }
    node *cur = peak->r;
    while (cur->l != NULL)
    {
        cur = cur->l;
    }
    peak->key = cur->key;
    del(cur);
}