Why Balanced Parentheses Problem Using Stack in DSA Python?

The Big Idea

What if a simple stack could save you hours of debugging mismatched brackets?

The Scenario

Imagine you are checking if a math expression typed by hand has matching parentheses. You try to count opening and closing brackets manually by scanning the expression from left to right.

The Problem

Counting manually is slow and easy to mess up, especially when parentheses are nested or mixed with different types like {}, [], (). You might miss a closing bracket or get confused about the order.

The Solution

Using a stack, you can push each opening bracket and pop it when you find a matching closing bracket. This keeps track of the order perfectly and quickly tells you if the parentheses are balanced.

Before vs After

✗ Before

expression = "(a+b)*(c-d))"
count = 0
for char in expression:
    if char == '(': count += 1
    elif char == ')': count -= 1
if count == 0:
    print("Balanced")
else:
    print("Not Balanced")

✓ After

expression = "(a+b)*(c-d))"
closing_to_open = {')': '(', ']': '[', '}': '{'}
stack = []
for char in expression:
    if char in '([{':
        stack.append(char)
    elif char in ')]}':
        if not stack or stack.pop() != closing_to_open[char]:
            print("Not Balanced")
            break
else:
    print("Balanced" if not stack else "Not Balanced")

What It Enables

This method lets you quickly and reliably check complex expressions for correct matching and nesting of parentheses.

Real Life Example

Compilers use this technique to verify that code blocks are properly opened and closed with braces, preventing syntax errors before running the program.

Key Takeaways

Manual counting fails with nested or mixed parentheses.

Stack remembers the order of opening brackets for matching.

Stack-based checking is fast, reliable, and essential in parsing code.