Day 25 — Valid Parentheses | Blind 75 | Java

Priyanka

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·

Aug 23, 2026

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Question

Given a string s containing only ()[]{}, determine if the string is valid.

A string is valid if:

• Every opening bracket has a matching closing bracket.
• Brackets are closed in the correct order.
• Brackets match the correct type.

Input & Output

Input:  s = "()"
Output: true

Input:  s = "()[]{}"
Output: true

Input:  s = "(]"
Output: false

Input:  s = "([)]"
Output: false

Input:  s = "([])"
Output: true

Approach

We use a Stack because brackets follow Last In, First Out (LIFO).

• If we see an opening bracket, push it into the stack.
• If we see a closing bracket, check whether it matches the top of the stack.
• If it doesn’t match, return false.
• At the end, the stack must be empty.

We use a HashMap to store the matching pairs:

) → (
} → {
] → [

Code

import java.util.*;

class Solution {
    public boolean isValid(String s) {
        Deque<Character> stack = new ArrayDeque<>();
        Map<Character, Character> resultMap = new HashMap<>();
        resultMap.put(')', '(');
        resultMap.put('}', '{')…