index.js

/**
 Given an expression string exp , write a program to examine whether the pairs and 
 the orders of “{“,”}”,”(“,”)”,”[“,”]” are correct in expression.

Example:
Input: exp = “[()]{}{[()()]()}”
Output: true

Input: exp = “[(])”
Output: false
*/

const Stack = require('../index');

function checkBalancedParenthesis(expression) {
  const s = new Stack();
  for (let i = 0; i < expression.length; i += 1) {
    const char = expression[i];
    if (char === '{' || char === '(' || char === '[') {
      // If current character is a starting bracket (‘(‘ or ‘{‘ or ‘[‘) then push it to stack
      s.push(char);
    } else {
      if (s.isEmpty()) {
        // when we have only right parenthesis or brackets in expresion
        return false;
      }
      if (
        (char === '}' && s.peek() !== '{') ||
        (char === ')' && s.peek() !== '(') ||
        (char === ']' && s.peek() !== '[')
      ) {
        return false;
      }
      // If the current character is a closing bracket (‘)’ or ‘}’ or ‘]’) then pop it from stack
      s.pop();
    }
  }
  if (s.isEmpty()) {
    // expression has balanced parenthesis
    return true;
  }
  return false;
}

module.exports = {
  checkBalancedParenthesis,
};