查找算法复习（1）--二分查找法

二分查找法要求被查找的线性表已经排序。

每一次查找，按中间索引把表分为左右两部分，通过对比中间值与目标值的大小，决定下一次查找在左表还是右表，直到无法再分割。

        public static int BinarySearch(string[] datalist, string key)
        {
            int low = 0;
            int high = datalist.Length - 1;//两个下标，决定查找的区间
            int middle;
            while (low <= high)//无法再分割就结束
            {
                middle = (low + high) / 2;//中间下标
                if (datalist[middle].CompareTo(key) > 0)//与中间值比较，缩小查找区间
                    high = middle - 1;
                else if (datalist[middle].CompareTo(key) < 0)
                    low = middle + 1;
                else
                    return middle;
            }
            return -1;
        }

使用

            string[] a = new string[] { "khlin", "hzluo", "jjguo", "hhchen", "jxhan", "lxiao", "jsxiao", "wwang", "lsxie", "lwang" };
           
            SelectedSort(a);
            foreach(string stra in a)
                Console.Write("{0}, ",stra);
            Console.WriteLine();
            string target1 = "jjguo";
            Console.WriteLine("{0} index: {1}", target1, BinarySearch(a, target1));
            string target2 = "lsxie";
            Console.WriteLine("{0} index: {1}", target2, BinarySearch(a, target2));
            string target3 = "hello";
            Console.WriteLine("{0} index: {1}", target3, BinarySearch(a, target3));