二分查找法 java

　　前几天去面试，让我写二分查找法，真是哔了狗！

　　提了离职申请，没事写写吧！

首先二分查找是在一堆有序的序列中找到指定的结果。

　　

public class Erfen
{
    public static int erfen(int a[], int key)
    {
        int start = 0;
        int end = a.length;
        while (start < end)
        {
            int mid = (start + end) / 2;

            if (key == a[mid])
            {
                System.out.println("@@");
                return mid;

            }
            else if (key < a[mid])
            {
                end = mid - 1;
                System.out.println(mid + "$$" + end);
            }
            else
            {
                start = mid + 1;
                System.out.println("&&");
            }
        }
        return -1;

    }

    public static int digui(int a[], int start, int end, int key)
    {
        if (start < end)
        {
            int mid = (start + end) / 2;
            if (key == a[mid])
            {
                return mid;
            }
            else if (key < a[mid])
            {
                digui(a, start, mid - 1, key);
            }
            else
            {
                digui(a, mid + 1, end, key);
            }
        }

        return -1;
    }

    public static void main(String[] args)
    {
        int[] a = { 1, 2, 3, 6, 8, 9 };
        System.out.println(a.length);
        int re = Erfen.erfen(a, 6);
        System.out.println(re);

        int ret = Erfen.digui(a, 0, 6, 6);
        System.out.println(ret);
    }

}