Valid Parentheses

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Given a string s containing just the characters '(', ')', '{', '}', '[' and ']', determine if the input string is valid.

An input string is valid if:

1. Open brackets must be closed by the same type of brackets.

2. Open brackets must be closed in the correct order.

3. Every close bracket has a corresponding open bracket of the same type.

Example 1:

Input: s = "()"
Output: true

Example 2:

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

Example 3:

Input: s = "(]"
Output: false

Constraints:

• 1 <= s.length <= 104

• s consists of parentheses only '()[]{}'.

You can solve this problem using a stack data structure. Here's a JavaScript implementation:

function isValid(s) {
    const stack = [];
    const matchingBrackets = {
        ')': '(',
        '}': '{',
        ']': '['
    };

    for (let i = 0; i < s.length; i++) {
        const char = s[i];
        
        if (char === '(' || char === '{' || char === '[') {
            stack.push(char);
        } else {
            if (stack.length === 0 || stack.pop() !== matchingBrackets[char]) {
                return false;
            }
        }
    }

    return stack.length === 0;
}

// Test cases
console.log(isValid("()"));      // Output: true
console.log(isValid("()[]{}"));  // Output: true
console.log(isValid("(]"));      // Output: false

This isValid function iterates through the given string s. For each character, if it's an opening bracket, it pushes it onto the stack. If it's a closing bracket, it checks if the stack is empty or if the corresponding opening bracket at the top of the stack matches the current closing bracket. If not, it returns false. Finally, it returns true if the stack is empty (meaning all opening brackets are closed properly).