深入剖析let/const在for循环中的作用原理

快速排序

'use strict';

const quickSort = function (array, low, high) {
  if (low >= high) {
    return;
  }
  let i = low;
  let j = high;
  const tmp = array[i];
  while (i < j) {
    while (i < j && array[j] >= tmp) {
      j--;
    }
    if (i < j) {
      array[i++] = array[j];
    }
    while (i < j && array[i] <= tmp) {
      i++;
    }
    if (i < j) {
      array[j--] = array[i];
    }
  }
  array[i] = tmp;
  quickSort(array, low, i - 1);
  quickSort(array, i + 1, high);
}

const arr = [1, 23, 7, 123, 45, 78, 10];
console.log(arr);
quickSort(arr, 0, arr.length - 1);
console.log(arr);

归并排序

'use strict';

// 两个有序数组合并
const memeryArray = function (arr1, arr2) {
  const c = [];
  let i = 0;
  let j = 0;
  let k = 0;
  while (i < arr1.length && j < arr2.length) {
    if (arr1[i] < arr2[j]) c[k++] = arr1[i++];
    else c[k++] = arr2[j++];
  }
  while (i < arr1.length) c[k++] = arr1[i++];
  while (j < arr2.length) c[k++] = arr2[j++];

  return c;
}

// 将同一数组，两段有序序列合并
const memery = function (arr, first, mid, last) {
  const temp = [];
  let i = first;
  const j = mid;
  let m = mid + 1;
  const n = last;
  let k = 0;
  while (i <= j && m <= n) {
    if (arr[i] < arr [m]) temp[k++] = arr[i++];
    else temp[k++] = arr[m++];
  }
  while (i <= j) temp[k++] = arr[i++];
  while (m <= n) temp[k++] = arr[m++];
  for (i = 0; i < k; i++) arr[first + i] = temp[i];
}

const mergeSort = function (arr, first, last) {
  if (!Array.isArray(arr)) throw new Error('argument is not a array');
  if (first < last) {
    const mid = parseInt((first + last) / 2, 10);
    mergeSort(arr, first, mid);
    mergeSort(arr, mid + 1, last);
    memery(arr, first, mid, last);
  }
};

const arr1 = [1, 7, 13, 20, 6, 9, 10, 10, 11, 26, 29];
console.log(arr1);
mergeSort(arr1, 0, arr1.length - 1);
console.log(arr1);