Given a string s that contains only '(', ')', '{', '}', '[', ']', determine whether the string is valid

I want to write a function that does the following: Given a string s that contains only '(', ')', '{', '}', '[', ']', determine whether the string is valid. A valid string needs to satisfy:

• the opening parenthesis must be closed with the same type of closing parenthesis.
• Opening parentheses must be closed in the correct order.
• Each closing parenthesis has a corresponding opening parenthesis of the same type.

Example:

Input: s = "()"
Output: true

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

Input: s = "(]"
Output: false.

But when I test the code with:
Input "()"
Output is showing as false.

Here is my code.

import java.util.HashMap;
import java.util.Map;

class Solution {
    public boolean isValid(String s) {
        Map<String, String> map = Map.of("(",")","[","]","{","}");

        if (s.length() % 2 != 0) {
            return false;
        }

        for (int index = 0; index < s.length() / 2; index++) {
            if (!map.containsKey(s.charAt(2 * index + 1))) {
                return false;
            } else {
                if (!map.get(s.charAt(2 * index + 1)).equals(s.charAt(2 * index + 2))) {
                    return false;
                }
            }
        }
        return true;
    }
}

The function may be realized by using the stack, but the first thing I thought of was my method. Where is the logic error in my method?

Looks like you have 2 issues:

1. Your code assumes charAt() takes index values from 1 onwards. It does not - it takes values from 0

2. Your code assumes there is no nesting. So, it won't work for cases like [()]

One additional issue that is not addressed in the first answer is that you are attempting to access a Map<String, String> with a char. charAt() returns a character and the keys in the map are strings. This can be fixed by updating the map to be Map<Character, Character>, or by getting the string value of the character (such as by using String.valueOf()) wherever you are getting the character at a certain index.

This combined with addressing the issues laid out in Abdeali's answer should fix your issue.