def part_two_fancy(ids):
    seen = set()
    for id in ids:
        #iteratively blank out each character in the id. Ex. "123" becomes "_23" and "1_3" and "12_"
        for i in range(len(id)):
            blanked_id = "".join("_" if idx==i else c for idx,c in enumerate(id))
            if blanked_id in seen:
                return blanked_id.replace("_", "")
            seen.add(blanked_id)