Problem

Stack Digit-Sum Filter

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python

Runtime

Python 3.11

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Stack Digit-Sum Filter

Use stack operations to remove numbers with the sum of digits being divisible by 6 or 7 but not both 6 and 7.

pythonPython 3.118 hidden tests

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solution.py

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stack = []
removed_stack = []

def push(value):
    """Add value to the top of stack and return None."""
    # TODO: Add value to the right side of stack.
    pass

def pop():
    """Remove and return the top value, or None when stack is empty."""
    # TODO: Handle both empty and non-empty stacks.
    pass

def display():
    """Return the top value of stack, or None when stack is empty."""
    # TODO: The only direct list index allowed for either stack is [-1].
    pass

def digit_sum(value):
    """Return the sum of the decimal digits of abs(value)."""
    # Examples: digit_sum(15) == 6 and digit_sum(-123) == 6.
    pass

def should_remove(value):
    """Return True when the digit sum is divisible by 6 or 7, but not both."""
    # Example: 15 is removed because its digit sum is 6.
    # Example: 34 is removed because its digit sum is 7.
    # Example: 348999 stays because its digit sum is 42, divisible by both.
    pass

def remove_special_numbers():
    """Discard special values and move every unspecial value to removed_stack."""
    # Use display() to inspect stack, then pop() to remove its top value.
    # After this function, stack is empty and removed_stack is temporary storage.
    pass

def add_back_unspecial_numbers():
    """Move values from removed_stack back to stack in their original order."""
    # Use push() for every value returned from removed_stack.
    pass

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