写了二分查找算法，欢迎查找算法bug

 

刚才看了《只有10%程序员能正确实现二分查找算法》文章http://news.csdn.net/a/20100423/218099.html，于是忍不住用C#写了个，欢迎查找算法的bug

 

二分查找可以解决（预排序数组的查找）问题：只要数组中包含T（即要查找的值），那么通过不断缩小包含T的范围，最终就可以找到它。一开始，范围覆盖整个数组。将数组的中间项与T进行比较，可以排除一半元素，范围缩小一半。就这样反复比较，反复缩小范围，最终就会在数组中找到T，或者确定原以为T所在的范围实际为空。对于包含N个元素的表，整个查找过程大约要经过log(2)N次比较。

 

/// <summary>
        /// 二分查找法
        /// </summary>
        /// <param name="aa"></param>
        /// <param name="a"></param>
        /// <returns></returns>
        public static int GetPosition(int[] aa, int a)
        {

            int arrLength = aa.Length;
            int startPosition = 0;
            int endPosition = arrLength - 1;
            int middlePosition = endPosition / 2;

            if (arrLength>0)
            {
                return GetValuePosition(aa, a, startPosition, endPosition, middlePosition);
            }

            return -1;

        }

        public static  int GetValuePosition(int[] aa,int a,int startPosition,int endPosition,int middlePosition)
        {
            if (a == aa[middlePosition])
            {
                return middlePosition;
            }
            if (a > aa[middlePosition]&&endPosition>=startPosition)
            {
                startPosition = middlePosition + 1;
                middlePosition = (endPosition + startPosition) / 2;
               return GetValuePosition(aa, a, startPosition, endPosition, middlePosition);

            }
            else if(a<aa[middlePosition]&&endPosition>=startPosition)
            {
                endPosition = middlePosition - 1;
                middlePosition = (endPosition + startPosition) / 2;
               return  GetValuePosition(aa, a, startPosition, endPosition, middlePosition);
            }

            return -1;

        }