算法 二分查找

原理很简单，二叉树的原理

       /// 

        /// 二分查找
        /// 
        /// 待查找的数组
        /// 要查找的数
        public static void erfen(int[] array, int val)
        {
            int leftIndex = 0;//查找起始下标
            int rightIndex = array.Length - 1;//数组终点下标，即最坏情况
            int currentIndex = 0;//当前查找的下标
            Array.Sort(array);//先升序排序
            //等起始<=终点时，可以继续查找
            while (leftIndex <= rightIndex)
            {
                currentIndex = (leftIndex + rightIndex) / 2;
                if (array[currentIndex] < val)
                {
                    leftIndex = currentIndex + 1;
                    Console.WriteLine(string.Format("下标{1}没找到！往后找！", currentIndex + 1,currentIndex));
                }
                else if (array[currentIndex] > val)
                {
                    rightIndex = currentIndex - 1;
                    Console.WriteLine(string.Format("下标{1}没找到！往前找！", currentIndex - 1, currentIndex));
                }
                else
                {
                    Console.WriteLine(string.Format("找到了！{0}在数组中的下标是{1}", val, currentIndex));
                    break;
                }
            }
            Console.WriteLine("不在数组中");
        }