BFE.devAI解答 - JavaScript 代码题
41. 手写Merge Sort

function mergeSort(arr) {
  if (arr.length < 2) {
    return arr;
  }
  const mid = Math.floor(arr.length / 2);
  const left = arr.slice(0, mid);
  const right = arr.slice(mid);
  return merge(mergeSort(left), mergeSort(right));
}

function merge(left, right) {
  const res = [];
  while (left.length && right.length) {
    if (left[0] <= right[0]) {
      res.push(left.shift());
    } else {
      res.push(right.shift());
    }
  }
  while (left.length) {
    res.push(left.shift());
  }
  while (right.length) {
    res.push(right.shift());
  }
  return res;
}

时间复杂度为O(nlogn)，空间复杂度为O(n)，是稳定排序。