Task with braces, brackets and parenthesis

Question

Task is to check if given string contains balanced sets of {}, [] and ().

For example, check(\"{[}]\") must return

Answer 1

Checking for nested braces seems like a natural case for std::stack. Push braces onto the stack as you iterate over the input and test for correct matches when you see a closing brace.

bool check(const std::string &expression) // balanced and nested?
{
    std::stack stack;

    for (auto ch : expression) {
        switch (ch) {
        case '(': // open parenthesis
        case '<': // open angle
        case '[': // open bracket
        case '{': // open brace
            stack.push(ch);
            break;
        case ')': // close parenthesis
            if (stack.empty() || stack.top() != '(') return false;
            stack.pop();
            break;
        case '>': // close angle
            if (stack.empty() || stack.top() != '<') return false;
            stack.pop();
            break;
        case ']': // close bracket
            if (stack.empty() || stack.top() != '[') return false;
            stack.pop();
            break;
        case '}': // close brace
            if (stack.empty() || stack.top() != '{') return false;
            stack.pop();
            break;
        }
    }
    return stack.empty(); // no unmatched braces left?
}