如何获得所有可能的数字，这些数字可以通过从现有数字中删除数字来实现？

def generate_numbers(current, remaining):
    if not remaining:
        print(current)
        return
    
    # Include the first digit and recurse
    generate_numbers(current + remaining[0], remaining[1:])
    
    # Exclude the first digit and recurse
    generate_numbers(current, remaining[1:])

# Example usage
original_number = "1234"
generate_numbers("", original_number)

def generate_numbers_iterative(original_number):
    stack = [("", original_number)]
    
    while stack:
        current, remaining = stack.pop()
        
        if not remaining:
            print(current)
            continue
        
        # Include the first digit
        stack.append((current + remaining[0], remaining[1:]))
        
        # Exclude the first digit
        stack.append((current, remaining[1:]))

# Example usage
original_number = "1234"
generate_numbers_iterative(original_number)