Valid Parentheses

Read the lesson → understand the pattern → then code. Tutor works offline (built-in teacher); optional Cursor/Gemini keys upgrade chat quality.

Topic refresher: Stack — Last In, First Out

LIFO for matching, undo, and next-greater patterns.

stack<char> st;
for (char c : s) {
    if (/* open */) st.push(c);
    else {
        if (st.empty() || st.top() != need) return false;
        st.pop();
    }
}
return st.empty();

Problems Stack & Monotonic Stack

Valid Parentheses

Easy

LeetCode

1/3

EasyStack & Monotonic StackLeetCode #20

Valid Parentheses

Stack of opens. On close, top must match. Empty at end.

Examples

Example 1

Input

()

Output

true

Example 2

Input

()[]{}

Output

true

Stuck? Take a nudge

C++17Autosaves