build_an_array_with_stack_operations.js

// Given an array target and an integer n. In each iteration, you will read a number from  list = {1,2,3..., n}.

// Build the target array using the following operations:

// Push: Read a new element from the beginning list, and push it in the array.
// Pop: delete the last element of the array.
// If the target array is already built, stop reading more elements.
// You are guaranteed that the target array is strictly increasing, only containing numbers between 1 to n inclusive.

// Return the operations to build the target array.

// You are guaranteed that the answer is unique.

 

// Example 1:

// Input: target = [1,3], n = 3
// Output: ["Push","Push","Pop","Push"]
// Explanation: 
// Read number 1 and automatically push in the array -> [1]
// Read number 2 and automatically push in the array then Pop it -> [1]
// Read number 3 and automatically push in the array -> [1,3]
// Example 2:

// Input: target = [1,2,3], n = 3
// Output: ["Push","Push","Push"]
// Example 3:

// Input: target = [1,2], n = 4
// Output: ["Push","Push"]
// Explanation: You only need to read the first 2 numbers and stop.
// Example 4:

// Input: target = [2,3,4], n = 4
// Output: ["Push","Pop","Push","Push","Push"]

/**
 * @param {number[]} target
 * @param {number} n
 * @return {string[]}
 */
var buildArray = function (target, n) {
  let output = [];
  i = 1;
  target.forEach((num) => {
    while (i !== num) {
      output.push("Push", "Pop");
      i++;
    }
    output.push("Push");
    i++;
  });
  return output;
};