c# 折半查找法实现代码

int[] a = new int[20] { 2, 3, 6, 7, 12, 18, 19, 21, 25, 28, 30, 33, 37, 39, 42, 45, 47, 49, 50, 51 };
            int x = 18, i;
            string j, k;
            var d = find(a, x, 0, 19);
            if (d == -1)
            {
                k = String.Format("未找到{0}", x);
            }
            else
            {
                for (i = 0; i < 20; i++)
                {
                    if ((i = d) > 0)
                    {
                        j = String.Format("{0}是第{1}个数\n", x, i + 1);
                        break;
                    }
                }
            }

find方法如下：

int find(int[] a, int x, int n, int m)
        {
            int i;
            if (n > m) return -1;
            i = (n + m) / 2;
            if (a[i] == x) return i;
            if (a[i] > x) return find(a, x, n, i - 1);
            return find(a, x, i + 1, m);
        }

可以输出j

  显示查找结果

    good luck ----------