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package com.hao.myrxjava;

/**

 * 折半查找 ：首先数组是已经排好序的

 *

 * @author zhanghaohao

 * @date 2017/5/15

 */

public class HalfDivision {

  /**

   * 循环实现

   *

   * @param array 排好序的数组

   * @param value 查找的值

   * @return value在array的位置

   */

  public static int halfDivision(int value, int[] array) {

    if (array == null || array.length == 0)

      throw new NullPointerException("array is null");

    int low = 0;

    int high = array.length - 1;

    int mid = (low+high)/2;

    while (array[mid] != value) {

      if (array[mid] > value)

        high = mid - 1;

      else

        low = mid + 1;

      if (low > high)

        return -1;

      mid = (low+high)/2;

      if (array[mid] == value)

        return mid;

    }

    return mid;

  }

  /**

   * 递归实现

   *

   * @param array 排好序的数组

   * @param value 查找的值

   * @param low 查找的起始位置

   * @param high 查找的末尾位置

   * @return value在array的位置

   */

  public static int halfDivision(int value, int[] array, int low, int high) {

    if (low > high)

      return -1;

    int mid = (low + high) / 2;

    if (array[mid] == value)

      return mid;

    else if (array[mid] > value)

      return halfDivision(value, array, low, mid - 1);

    else if (array[mid] < value)

      return halfDivision(value, array, mid+1, high);

    return -1;

  }

}