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How to efficiently determine if the grouping symbols of an expression match up correctly, in Python?

Wissam answered on July 16, 2022 Popularity 3/10 Helpfulness 8/10

answer How to efficiently determine if the grouping symbols of an expression match up correctly, in Python?

How to efficiently determine if the grouping symbols of an expression match up correctly, in Python?

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"""
This implementation demonstrates how 
to efficiently determine if the opening
and closing brackets of an arithmetic
expression match up correctly.

Example: 
For following expression: (1 + 2)
The output would be: true
However, for the following one: (1 + 2]
The output would be: false

Let n be the number of tokens that make up
the arithmetic expression.

Time complexity: O(n)
Space complexity: O(n)
"""


def validate_expression(expression):
    opening_symbols = "([{"
    closing_symbols = ")]}"
    # A map associating opening with closing
    matching_symbols = {")": "(", "]": "[", "}": "{"}
    stack = []
    for token in expression:
        # Add an opening symbol to stack
        if token in opening_symbols:
            stack.append(token)
        elif token in closing_symbols:
            # For a closing symbol stack cannot be empty
            if is_empty(stack):
                return False
            if stack[-1] == matching_symbols[token]:
                # If closing symbol match opening at top of stack
                # pop the top element
                stack.pop()
            else:
                # Closing and opening don't match up
                return False
    # Stack should be empty after processing all tokens
    return is_empty(stack)


def is_empty(stack):
    return len(stack) == 0


print(validate_expression("([1 + 2])"))  # True
print(validate_expression("([1 + 2)"))  # False

Popularity 3/10 Helpfulness 8/10 Language python

Source: Grepper

Tags: expression grouping match matching python symbols

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Contributed on Jul 16 2022

Wissam

0 Answers Avg Quality 2/10

How to efficiently determine if the grouping symbols of an expression match up correctly, in Python?

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