def my_approach(a):

    tot_samples = len(a)
    choices = set(range(5000)).difference(a)

    replacements = defaultdict(list)
    first_seen = True
    current_chain = []

    for i, val in enumerate(a):
        if i == tot_samples - 1:
            current_chain.append(i)
            if a[-1] == current_chain[-1]:
                current_chain.append(i+1)
                replacements[val].append(current_chain)
            else:
                replacements[a[-1]].append([i])
            break

        if first_seen:
            current_chain.append(i)
            first_seen = False

        if a[i+1] == val:
            current_chain.append(i+1)
        else:
            replacements[val].append(current_chain)
            current_chain = []
            first_seen = True

    for k, v in replacements.items():
        if len(v) > 1:
            for chunk in range(1, len(v)):
                replacement_val = random.choice(list(choices))
                choices.add(replacement_val)
                for index in v[chunk]:
                    a[index] = replacement_val