package com.hao.myrxjava;

/**
 * 折半查找 ：首先數(shù)組是已經(jīng)排好序的
 *
 * @author zhanghaohao
 * @date 2017/5/15
 */

public class HalfDivision {

  /**
   * 循環(huán)實(shí)現(xiàn)
   *
   * @param array 排好序的數(shù)組
   * @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;
  }

  /**
   * 遞歸實(shí)現(xiàn)
   *
   * @param array 排好序的數(shù)組
   * @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;
  }
}