Find family members who have no parents or exactly one parent.

"""
Given a list of (parent, child) relationships, return a sorted list of family members who have no parents or exactly one parent.
"""
from collections import defaultdict

def find_family_members(relations: list[tuple[str, str]]) -> list[str]:
    in_degree = defaultdict(int)
    all_members = set()

    # Populate in-degree and collect all members
    for parent, child in relations:
        in_degree[child] += 1
        all_members.add(parent)
        all_members.add(child)

    # Members that appear only as parents have in-degree 0
    # Members that never appear as children also have in-degree 0
    # So ensure to set in-degree for all members not present in in_degree
    for member in all_members:
        if member not in in_degree:
            in_degree[member] = 0

    # Collect members with in-degree 0 or 1
    result = [member for member, degree in in_degree.items() if degree <= 1]

    # Return sorted list for consistency
    return sorted(result)

# Example Usage:
if __name__ == "__main__":
    # Example input: list of (parent, child) relationships
    relationships = [
        ("John", "Mary"),
        ("John", "Alice"),
        ("Mary", "Bob"),
        ("Alice", "Bob"),
        ("Eve", "John"),
        ("Eve", "Mary"),
        # Introducing a cycle
        ("Bob", "Eve")
    ]

    members = find_family_members(relationships)
    print("Family members with 0 or 1 parent:")
    for member in members:
        print(member)