Valid Parentheses | LeetCode 20

[Written explanation coming soon.]

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Here is the full implementation.

/**
 * @param {string} s
 * @return {boolean}
 */
let isValid = function(s) {
  let stack = new Stack();

  for (let character of s) {
    if (character === '{' || character === '[' || character === '(') {
      stack.push(character);
    } else if (!stack.isEmpty() && character === '}' && stack.peek() === '{') {
      stack.pop();
    } else if (!stack.isEmpty() && character === ')' && stack.peek() === '(') {
      stack.pop();
    } else if (!stack.isEmpty() && character === ']' && stack.peek() === '[') {
      stack.pop();
    } else {
      return false;
    }
  }

  return stack.isEmpty();
};



class Stack {
  constructor() {
    this.count = 0;
    this.storage = {};
  }

  push(val) {
    this.storage[this.count] = val;
    this.count++;
  }

  getCount() {
    return this.count;
  }

  pop() {
    if (this.count === 0) {
      return undefined;
    }

    this.count--;
    let result = this.storage[this.count];
    delete this.storage[this.count];
    return result;
  }

  peek() {
    let result = this.storage[this.count - 1];
    return result;
  }

  isEmpty() {
    return this.count === 0;
  }
}