Are the brackets balanced?

Challenge

Check that all brackets in a string are correctly matched and nested.

Task

Implement int balanced_brackets(const char *s) that returns 1 if the brackets in s are correctly matched and nested, else 0. Recognised pairs are (), [], and {}; all other characters are ignored.

Input

s: a NUL-terminated string that may contain brackets and any other characters.

Output

int: 1 if balanced, 0 otherwise.

Example

"()"             ->   1
"(a + [b * c])"  ->   1
"{[()]}"         ->   1
"(]"             ->   0   (mismatched closer)
"("              ->   0   (unclosed)
")"              ->   0   (closer with no opener)
""               ->   1   (empty is balanced)

Edge cases

• Empty string is balanced (returns 1).
• A closer with no matching opener fails immediately.
• An opener never closed fails at end of string.

Rules

• Use an array as a stack; assume a maximum nesting depth of 512.

Why this matters

A stack-based bracket checker is the simplest non-trivial use of a stack and a great warm-up for full expression parsers. The same logic powers IDE bracket-matching, JSON validators, and shell quoting checkers.

Input format

s: a NUL-terminated string; non-bracket characters are ignored.

Output format

int: 1 if brackets are balanced, else 0.

Constraints

s is a null-terminated string containing bracket characters.

Starter code

int balanced_brackets(const char *s) { /* TODO */ return 0; }

Common mistakes

Stack underflow when encountering closing bracket with empty stack.

Edge cases to handle

Empty string, string with only openers, string with only closers, mismatched types.

Complexity

O(strlen).

Background lessons

• Stacks
• Loops: for / while / do-while

Up next

• A FIFO queue implemented with two stacks
• Fixed-capacity circular queue