编程之美书摘

Posted 2020-08-26 Hello Long

static void Main(string[] args)
        {
            char[] arr = new[] { ‘a‘, ‘b‘, ‘c‘, ‘d‘, ‘e‘};
            char v = ‘d‘;
            var index = BiSearch(arr, 0, 4, v);
            Console.WriteLine(index);

            char[] arr2 = new[] {  ‘b‘, ‘c‘, ‘d‘, ‘e‘, ‘f‘ };
            char v2 = ‘a‘;
            var index2 = BiSearch(arr2, 0, 4, v2);
            Console.WriteLine(index2);
            Console.Read();
        }


        static int BiSearch(char[] arr, int b, int e, char v)
        {
            int minIndex = b, maxIndex = e, midIndex;

            //循环结束有两种情况：
            //若minIndex为偶数则minIndex == maxIndex
            //否则就是minIndex == maxIndex - 1
            while (minIndex < maxIndex - 1)
            {
                midIndex = minIndex + (maxIndex - minIndex)/2;
                if (arr[midIndex].CompareTo(v) <= 0)
                {
                    minIndex = midIndex;
                }
                else
                {
                    //不需要midIndex - 1,防止minIndex == maxIndex
                    maxIndex = midIndex;
                }
            }

            if (arr[maxIndex].CompareTo(v) == 0)
            {
                return maxIndex;
            }
            else if (arr[minIndex].CompareTo(v) == 0)
            {
                return minIndex;
            }
            else
            {
                return -1;
            }
        }