二分查找、折半查找

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;
    }
}