这算O(n)还是O(logn)?

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转换字符串为浮点数

namespace ConsoleApplication1{    class TestFaiureException : Exception    {        public TestFaiureException(string s)            : base(s)        {         }    }    class MyUtils    {        public static void _Main(string[] args)        {            string[] testData = new string[] { "123", "-123", "123.1", "-123.1", "0", "0.1", "1.2.3", "-.3", "0.a", ".1" };            double[] expected = new double[] { 123, -123, 123.1, -123.1, 0, 0.1, 0, 0, 0, 0 };            try            {                delegateConvertToFloat dctf = ConvertToFloat;                for (int i = 0; i < testData.Length; i++)                {                    TestConvertToFloat(dctf, testData[i], expected[i]);                }            }            catch (Exception ex)            {                Console.WriteLine(ex.ToString());            }        }        delegate double delegateConvertToFloat(string s);        private static void TestConvertToFloat(delegateConvertToFloat func, string input, double expected)        {            try            {                double actual = func(input);                if (expected == actual)                {                    return;                }                else                {                    throw new TestFaiureException(string.Format("expected: {0}, actual: {1}", expected.ToString(), actual));                }            }            catch (FormatException ex)            {                Console.WriteLine(ex.Message);            }            catch (TestFaiureException ex)            {                Console.WriteLine(ex.Message);            }        }        private static double ConvertToFloat(string s)        {            if (string.IsNullOrEmpty(s))            {                throw new ArgumentNullException("s");            }            string pattern = @"^[+-]?\d+(\.\d+)?$";            if (!Regex.IsMatch(s, pattern, RegexOptions.Singleline))            {                throw new FormatException("not legal digit: " + s);            }            string digits;            bool isNagative = false;            if (s.StartsWith("+"))            {                digits = s.Substring(1);            }            else if (s.StartsWith("-"))            {                digits = s.Substring(1);                isNagative = true;            }            else            {                digits = s;            }            int dot = digits.IndexOf(".");            int ldot;            int rdot;            if (dot == -1)            {                dot = digits.Length;                ldot = digits.Length - 1;                rdot = digits.Length;            }            else            {                ldot = dot - 1;                rdot = dot + 1;            }                        int len = digits.Length;            double lResult = 0;            double rResult = 0;            while (ldot >= 0 || rdot < len)            {                if (ldot >= 0)                {                    lResult = lResult + (digits[ldot] - '0') * Math.Pow(10, (dot - 1) - ldot);                    ldot--;                }                if (rdot < len)                {                    rResult = rResult + (digits[rdot] - '0') * Math.Pow(10, dot - rdot);                    rdot++;                }            }            return isNagative ? (-1) * (lResult + rResult) : (lResult + rResult);        }    }}

这才是真正的O(N)

class StringToFloat    {        private static bool InternalValidate(string strFloat)        {            return true;        }        public static double ConvertTodouble(string s)        {            if (!InternalValidate(s))            {                throw new FormatException(s);            }            double sum1 = 0;            double sum2 = 0;            bool meetDot = false;            int dotIndex = 1;            for (int i = 0; i < s.Length; i++)            {                if (s[i] == '.')                {                    meetDot = true;                    continue;                }                if (!meetDot)                {                    sum1 = sum1 * 10 + (s[i] - '0');                    continue;                }                if (meetDot)                {                    sum2 = sum2 + (s[i] - '0') * Math.Pow(0.1, dotIndex);                    dotIndex++;                    continue;                }            }            return sum1 + sum2;        }    }