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---

title: 冒泡排序
date: 2020-12-07 14:37:27

tags:

冒泡排序最坏效率：O(N²)
冒泡排序平均效率：
冒泡排序最好效率：

冒泡排序步骤如下。

1. 指向数组中两个相邻的元素（最开始是数组的头两个元素），比较它们的大小。
2. 如果它们的顺序错了（即左边的值大于右边），就互换位置。如果顺序已经是正确的，那这一步就什么都不用做。  
3. 将两个指针右移一格。重复第(1)步和第(2)步，直至指针到达数组末尾。
4. 重复第(1)至(3)步，直至从头到尾都无须再做交换，这时数组就排好序了。

class BubbleSort extends Sort {
  sort(originalArray) {
    // Flag that holds info about whether the swap has occur or not.
    let swapped = false;
    // Clone original array to prevent its modification.
    const array = [...originalArray];

    for (let i = 1; i < array.length; i += 1) {
      swapped = false;

      // Call visiting callback.
      this.callbacks.visitingCallback(array[i]);

      for (let j = 0; j < array.length - i; j += 1) {
        // Call visiting callback.
        this.callbacks.visitingCallback(array[j]);

        // Swap elements if they are in wrong order.
        if (this.comparator.lessThan(array[j + 1], array[j])) {
          [array[j], array[j + 1]] = [array[j + 1], array[j]];

          // Register the swap.
          swapped = true;
        }
      }

      // If there were no swaps then array is already sorted and there is
      // no need to proceed.
      if (!swapped) {
        return array;
      }
    }

    return array;
  }
}

class Sort {
  constructor(originalCallbacks) {
    this.callbacks = Sort.initSortingCallbacks(originalCallbacks);
    this.comparator = new Comparator(this.callbacks.compareCallback);
  }

  /**
   * @param {SorterCallbacks} originalCallbacks
   * @returns {SorterCallbacks}
   */
  static initSortingCallbacks(originalCallbacks) {
    const callbacks = originalCallbacks || {};
    const stubCallback = () => {};

    callbacks.compareCallback = callbacks.compareCallback || undefined;
    callbacks.visitingCallback = callbacks.visitingCallback || stubCallback;

    return callbacks;
  }

  sort() {
    throw new Error('sort method must be implemented');
  }
}

class Comparator {
  /**
   * @param {function(a: *, b: *)} [compareFunction] - It may be custom compare function that, let's
   * say may compare custom objects together.
   */
  constructor(compareFunction) {
    this.compare = compareFunction || Comparator.defaultCompareFunction;
  }

  /**
   * Default comparison function. It just assumes that "a" and "b" are strings or numbers.
   * @param {(string|number)} a
   * @param {(string|number)} b
   * @returns {number}
   */
  static defaultCompareFunction(a, b) {
    if (a === b) {
      return 0;
    }

    return a < b ? -1 : 1;
  }

  /**
   * Checks if two variables are equal.
   * @param {*} a
   * @param {*} b
   * @return {boolean}
   */
  equal(a, b) {
    return this.compare(a, b) === 0;
  }

  /**
   * Checks if variable "a" is less than "b".
   * @param {*} a
   * @param {*} b
   * @return {boolean}
   */
  lessThan(a, b) {
    return this.compare(a, b) < 0;
  }

  /**
   * Checks if variable "a" is greater than "b".
   * @param {*} a
   * @param {*} b
   * @return {boolean}
   */
  greaterThan(a, b) {
    return this.compare(a, b) > 0;
  }

  /**
   * Checks if variable "a" is less than or equal to "b".
   * @param {*} a
   * @param {*} b
   * @return {boolean}
   */
  lessThanOrEqual(a, b) {
    return this.lessThan(a, b) || this.equal(a, b);
  }

  /**
   * Checks if variable "a" is greater than or equal to "b".
   * @param {*} a
   * @param {*} b
   * @return {boolean}
   */
  greaterThanOrEqual(a, b) {
    return this.greaterThan(a, b) || this.equal(a, b);
  }

  /**
   * Reverses the comparison order.
   */
  reverse() {
    const compareOriginal = this.compare;
    this.compare = (a, b) => compareOriginal(b, a);
  }
}