选择排序

选择排序最坏效率：O(N²)
选择排序平均效率：
选择排序最好效率：

选择排序的步骤如下。

1. 从左至右检查数组的每个格子，找出值最小的那个。在此过程中，我们会用一个变量来记住检查过的数字的最小值。如果一个格子中的数字比记录的最小值还要小，就把变量改成该格子的索引。
2. 知道哪个格子的值最小之后，将该格与本次检查的起点交换。第1次检查的起点是索引0，第2次是索引1，以此类推。
3. 重复第(1)(2)步，直至数组排好序。

class SelectionSort extends Sort {
  sort(originalArray) {
    // Clone original array to prevent its modification.
    const array = [...originalArray];

    for (let i = 0; i < array.length - 1; i += 1) {
      let minIndex = i;

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

      // Find minimum element in the rest of array.
      for (let j = i + 1; j < array.length; j += 1) {
        // Call visiting callback.
        this.callbacks.visitingCallback(array[j]);

        if (this.comparator.lessThan(array[j], array[minIndex])) {
          minIndex = j;
        }
      }

      // If new minimum element has been found then swap it with current i-th element.
      if (minIndex !== i) {
        [array[i], array[minIndex]] = [array[minIndex], array[i]];
      }
    }

    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);
  }
}