Solution.js

/**
 * @param {number[]} nums
 * @return {number}
 */

/**
 * Author: Mcnwork2018
 */

var arrayPairSum = function (nums) {
  let result = merge_sort(nums);
  let sum = 0;
  for (let i = 0; i < result.length; i += 2) {
    sum += result[i];
  }
  return sum;
};
function merge_sort(A) {
  let len = A.length;
  if (len === 1) return A;
  let mid = ~~(len / 2);
  let leftArray = A.slice(0, mid);
  let rightArray = A.slice(mid, len);
  return merge(merge_sort(leftArray), merge_sort(rightArray));
}
function merge(left, right) {
  let i = 0,
    j = 0,
    k = 0,
    tmp = [];
  while (i < left.length && j < right.length) {
    if (left[i] <= right[j]) {
      tmp[k++] = left[i++];
    } else {
      tmp[k++] = right[j++];
    }
  }
  while (i < left.length) {
    tmp[k++] = left[i++];
  }
  while (j < right.length) {
    tmp[k++] = right[j++];
  }
  return tmp;
}