二分查找

        int GetVal(int[] arry, int fval, int begin, int end)
        {
            if (Math.Abs(begin - end) == 1) return -1;
            int mid = (begin + end) / 2;
            if (arry[mid] < fval)
                return GetVal(arry, fval, mid, end);
            else if (arry[mid] > fval)
                return GetVal(arry, fval, begin, mid);
            else if (arry[mid] == fval)
                return arry[mid];
            else
                return -1;//no result value
        }