Are the brackets balanced?

Challenge

Implement int balanced_brackets(const char *s) returning 1 if the string s has correctly nested and matched brackets, else 0.

Bracket pairs recognised: (), [], {}.

All non-bracket characters are ignored.

Examples

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

Edge cases

• Empty string is balanced (vacuously).
• A closer without an opener is an immediate failure.
• An opener never closed is a failure at end-of-string.

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

Null-terminated string.

Output format

1/0.

Constraints

Use a stack (array). Maximum nesting depth assumed <= 512.

Starter code

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

Common mistakes

Just counting openers vs closers — fails on (]). Forgetting to check the stack is non-empty before peeking on a closer.

Edge cases to handle

Empty; only openers; only closers; deeply nested; mixed bracket types.

Complexity

O(strlen).

Background lessons

• Stacks
• for / while / do-while

Up next

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