二分查找算法

package com.chenjun.mysite.module.sys.service;

/**
 * 
 * @author Administrator
 *
 */
public class 二分查找类2
{

    private static final int size = 10;

    public static void main(String[] args)
    {
        int[] a = new int[size];
        for (int i = 0; i < size; i++)
        {
            a[i] = (2 * i) + 1;
        }
        // 1,3,5,7,9,11
        for (int i = 0; i < size; i++)
        {
            System.out.print(a[i] + ",");
        }
        System.out.println("最终下标 " + binarySearch(7, a, 0, size - 1));
    }

    // 返回找到的下标
    public static int binarySearch(int number, int[] arr, int 小下标, int 大下标)
    {

        int 中间下标 = (大下标 + 小下标) / 2;
        if (number > arr[中间下标])
        {
            小下标 = 中间下标 + 1;
            // 递归
            return binarySearch(number, arr, 小下标, 大下标);
        }
        else if (number < arr[中间下标])
        {
            大下标 = 中间下标 - 1;
            return binarySearch(number, arr, 小下标, 大下标);
        }
        else
        {
            return 中间下标;
        }
    }
}

 

 JDK1.7里面的实现，源自Arrays.class文件

private static int binarySearch0(long[] a, int fromIndex, int toIndex, long key)
    {
        int low = fromIndex;
        int high = toIndex - 1;

        while (low <= high)
        {
            int mid = (low + high) >>> 1;
            long midVal = a[mid];

            if (midVal < key)
                low = mid + 1;
            else if (midVal > key)
                high = mid - 1;
            else
                return mid; // key found
        }
        return -(low + 1); // key not found.
    }