Problem16.js

// Problem 16
//
// This problem was asked by Twitter.
//
// You run an e-commerce website and want to record the last N order ids in a log.
//
// Implement a data structure to accomplish this, with the following API:
//
// record(order_id): adds the order_id to the log
// get_last(i): gets the ith last element from the log. i is guaranteed to be smaller than or equal to N.
// You should be as efficient with time and space as possible.
//
// Log takes O(N) Space due to size
// record and getLast is O(1) Time complexity

class Log {
  /**
   * Creates a Log. Initializes circular buffer with size
   * @param {number} size
   */
  constructor(size) {
    this.size = size;
    this.logArr = [];
    this.currIndex = 0;
  }

  /**
   * Adds the order id to the log.
   * @param {number} orderId
   */
  record(orderId) {
    this.logArr[this.currIndex] = orderId;
    this.currIndex = (this.currIndex + 1) % this.size;
  }

  /**
   * Gets the ith last element.
   * @param {number} i
   * @return {number}
   */
  getLast(i) {
    return this.logArr[(this.currIndex - i + this.size) % this.size];
  }
}

export default Log;