Q101- Code: Write a code for Valid Parentheses in JavaScript

Check if a string containing only parentheses ()[]{} is valid.
A string is valid if:

1. Open brackets are closed by the same type of brackets
2. Open brackets are closed in the correct order

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Solution using Stack

function isValidParentheses(s) {
  const stack = [];
  const map = {
    "(": ")",
    "{": "}",
    "[": "]"
  };

  for (let char of s) {
    if (map[char]) {
      // If it's an opening bracket, push the expected closing bracket
      stack.push(map[char]);
    } else {
      // If it's a closing bracket, it must match the top of the stack
      if (stack.pop() !== char) {
        return false;
      }
    }
  }

  // Stack should be empty if all brackets are matched
  return stack.length === 0;
}

// Example usage
console.log(isValidParentheses("()"));       // true
console.log(isValidParentheses("()[]{}"));   // true
console.log(isValidParentheses("(]"));       // false
console.log(isValidParentheses("([{}])"));   // true
console.log(isValidParentheses("((("));      // false

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Explanation:

1. Stack Approach:
   • Push expected closing brackets when encountering an opening bracket.
   • When encountering a closing bracket, check if it matches the top of the stack.
2. Validation:
   • If the stack is empty at the end → all brackets matched.
   • If not → invalid parentheses.
3. Time Complexity:
   • O(n), where n = length of the string
4. Space Complexity:
   • O(n) for the stack

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⚡ In short:

Use a stack to track expected closing brackets; validate each closing bracket against the stack. If the stack is empty at the end, the parentheses are valid.