Lista

def smallestPossible(num):
    "do not use at the start"
    return [0 if i == "?" else int(i) for i in num]


def lowestLarger(prev, num, eka=False):
    if (not prev) and (not num):
        return []
    if eka and len(prev) > len(num):
        return None
    if eka and len(prev) < len(num):
        return [1 if num[0] == "?" else int(num[0])] + smallestPossible(num[1:])
    # both have the same length
    if num[0] == "?":
        a = lowestLarger(prev[1:], num[1:])
        if a is None:
            if prev[0] + 1 < 10:
                return [prev[0] + 1] + smallestPossible(num[1:])
            else:
                return None
        else:
            if a:  # if the length is not 0
                return [prev[0]] + a
            elif prev[0] + 1 < 10:
                return [prev[0] + 1]
            else:
                return None

    else:
        first = int(num[0])
        if first < prev[0]:
            return None
        elif first == prev[0]:
            a = lowestLarger(prev[1:], num[1:])
            if a is not None:
                if a:
                    return [first] + a
                else:
                    return None
            else:
                return None
        else:
            return [first] + smallestPossible(num[1:])

    raise


def main():
    n = int(input())
    L = [[0]]
    impossible = False
    for _ in range(n):
        num = list(input())
        if impossible:
            continue
        L.append(lowestLarger(L[-1], num, True))
        if L[-1] is None:
            impossible = True
    if impossible:
        print("IMPOSSIBLE")
    else:
        for i in L[1:]:
            # print("".join(str(j) for j in i))
            print(*i, sep="")


if __name__ == "__main__":
    main()

Test 1

Group: 1, 2, 3

Verdict: ACCEPTED

Test 2

Group: 2, 3

Verdict: ACCEPTED

Test 3

Group: 3

Verdict: ACCEPTED

Test 4

Group: 1, 2, 3

Verdict: ACCEPTED

Test 5

Group: 1, 2, 3

Verdict: ACCEPTED

Test 6

Group: 1, 2, 3

Verdict: ACCEPTED

Test 7

Group: 1, 2, 3

Verdict: ACCEPTED

Test 8

Group: 3

Verdict: ACCEPTED

Test 9

Group: 3

Verdict: ACCEPTED

Test 10

Group: 3

Verdict: ACCEPTED