PUSH (add to top) POP (remove from top)
│ ▲
▼ │
┌──────────────┐ ┌──────────────┐
│ Item 3 │ ◄── TOP ──► │ Item 3 │ (Popped first)
├──────────────┤ ├──────────────┤
│ Item 2 │ │ Item 2 │
├──────────────┤ ├──────────────┤
│ Item 1 │ │ Item 1 │
└──────────────┘ └──────────────┘Can adapt std::deque (default), std::vector, or std::list.
#include <iostream>
#include <stack>
#include <string>
bool areBracketsBalanced(const std::string& expr) {
std::stack<char> s;
for (char ch : expr) {
if (ch == '(' || ch == '{' || ch == '[') {
s.push(ch);
} else if (ch == ')' || ch == '}' || ch == ']') {
if (s.empty()) return false;
char top = s.top();
if ((ch == ')' && top == '(') ||
(ch == '}' && top == '{') ||
(ch == ']' && top == '[')) {
s.pop();
} else {
return false;
}
}
}
return s.empty();
}
int main() {
std::string test1 = "{[()]}()";
std::string test2 = "{[(])}";
std::cout << test1 << " -> " << (areBracketsBalanced(test1) ? "Balanced" : "Invalid") << "\n";
std::cout << test2 << " -> " << (areBracketsBalanced(test2) ? "Balanced" : "Invalid") << "\n";
return 0;
}std::stack for syntax parsing, expression evaluation (Reverse Polish Notation), and DFS traversal..empty() before calling .top() or .pop() to prevent segmentation faults.emplace() for constructing objects directly on the stack without copies.