// https://www.freecodecamp.org/learn/coding-interview-prep/algorithms/implement-merge-sort

function mergeSort(array) {
  // Only change code below this line
  let merges = Math.floor(array.length / 2);
  let mergeSize = 1;
  let stop = false;
  while (!stop) {
    stop = merges ? false : true;
    const array2 = [];
    for (let i = 0; i <= merges; i++) {
      const leftArrayStart = i * mergeSize * 2;
      const rightArrayStart = leftArrayStart + mergeSize;
      const leftArrayEnd = Math.min(rightArrayStart, array.length);
      const rightArrayEnd = Math.min(rightArrayStart + mergeSize, array.length);
      let leftI = leftArrayStart; // left array pointer
      let rightI = rightArrayStart; // right array pointer
      while (leftI < leftArrayEnd && rightI < rightArrayEnd) {
        if (array[leftI] <= array[rightI]) {
          array2.push(array[leftI++]);
        } else {
          array2.push(array[rightI++]);
        }
      }
      while (leftI < leftArrayEnd) {
        array2.push(array[leftI++]);
      }
      while (rightI < rightArrayEnd) {
        array2.push(array[rightI++]);
      }
    }

    array = array2;
    mergeSize *= 2;
    merges = Math.floor(merges / 2);
  }
  return array;
  // Only change code above this line
}

console.log(mergeSort([4, 2, 1, 6, 5, 3, 0]));
console.log(
  mergeSort([
    1, 4, 2, 8, 345, 123, 43, 32, 5643, 63, 123, 43, 2, 55, 1, 234, 92,
  ])
);