1441-build-an-array-with-stack-operations.js

/**
 * 1441. Build an Array With Stack Operations
 * https://leetcode.com/problems/build-an-array-with-stack-operations/
 * Difficulty: Medium
 *
 * You are given an integer array target and an integer n.
 *
 * You have an empty stack with the two following operations:
 * - "Push": pushes an integer to the top of the stack.
 * - "Pop": removes the integer on the top of the stack.
 *
 * You also have a stream of the integers in the range [1, n].
 *
 * Use the two stack operations to make the numbers in the stack (from the bottom to the top) equal
 * to target. You should follow the following rules:
 * - If the stream of the integers is not empty, pick the next integer from the stream and push it
 *   to the top of the stack.
 * - If the stack is not empty, pop the integer at the top of the stack.
 * - If, at any moment, the elements in the stack (from the bottom to the top) are equal to target,
 *   do not read new integers from the stream and do not do more operations on the stack.
 *
 * Return the stack operations needed to build target following the mentioned rules. If there are
 * multiple valid answers, return any of them.
 */

/**
 * @param {number[]} target
 * @param {number} n
 * @return {string[]}
 */
var buildArray = function(target, n) {
  const result = [];
  let current = 1;

  for (const num of target) {
    while (current < num) {
      result.push('Push');
      result.push('Pop');
      current++;
    }
    result.push('Push');
    current++;
  }

  return result;
};