// 给的一个数组----.前提：--->数组必须是有序的

    int[] arr = {1, 3, 5, 7, 9, 11, 13};

    int index = binarySearch( arr, 8, 0, arr.length -1 );

    System.out.println( index );

}

public static int binarySearch(int[] arr, int item, int low, int higt) {

if (low > higt) {//递归结束条件

        return -1;

    }

System.out.println("------" );

    int mid = (low + higt) /2;

    int guess = arr[mid];//永远瞎猜，猜中间数

    if (guess > item) {

return binarySearch( arr, item, low, mid -1 );

    }else if (guess == item) {

return mid;

    }else {

return binarySearch( arr, item, mid +1, higt );

    }

}