以下是我对此的看法，使用迭代和递归进行运行时间分析。
public static class IntegerToString
{
static char[] d = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ".ToCharArray();
public static string Iteration(int num, int radix = 10)
{
if (num == 0) return "0";
if (num < 0) return "-" + Iteration(Math.Abs(num));
var r = new List<char>();
while (num > 0)
{
r.Insert(0, d[num % radix]);
num /= radix;
}
return new string(r.ToArray());
}
public static string Recursion(int num, int radix = 10)
{
if (num == 0) return "0";
if (num < 0) return "-" + Recursion(Math.Abs(num));
return (num > radix - 1 ? Recursion(num / radix) : "") + d[num % radix];
}
}
要点
- 支持2到36进制转换（注意：你必须确保输入的进制是正确的，因为没有异常处理）
- 递归方法只有3行代码！（类似代码高尔夫）
分析
下面是两种方法与我的电脑上标准 ToString() 方法的运行时间对比的分析。
50 runs of 100000 items per set
Running Time:
Iteration: 00:00:02.3459591 (00:00:00.0469191 avg)
Recursion: 00:00:02.1359731 (00:00:00.0427194 avg)
Standard : 00:00:00.4271253 (00:00:00.0085425 avg)
Ratios:
| Iter | Rec | Std
-----+------+------+-----
Iter | 1.00 | 0.91 | 0.18
Rec | 1.10 | 1.00 | 0.20
Std | 5.49 | 5.00 | 1.00
结果表明，迭代和递归方法的运行速度比标准的ToString()方法慢了5.49倍和5.00倍。
以下是我用于分析的代码：
class Program
{
static void Main(string[] args)
{
var r = new Random();
var sw = new System.Diagnostics.Stopwatch();
var loop = new List<long>();
var recr = new List<long>();
var std = new List<long>();
var setSize = 100000;
var runs = 50;
Console.WriteLine("{0} runs of {1} items per set", runs, setSize);
for (int j = 0; j < runs; j++)
{
var numbers = Enumerable.Range(1, setSize)
.Select(s => r.Next(int.MinValue,
int.MaxValue))
.ToArray();
sw.Start();
for (int i = 0; i < setSize; i++)
IntegerToString.Iteration(numbers[i]);
sw.Stop();
loop.Add(sw.ElapsedTicks);
sw.Reset();
sw.Start();
for (int i = 0; i < setSize; i++)
IntegerToString.Recursion(numbers[i]);
sw.Stop();
recr.Add(sw.ElapsedTicks);
sw.Reset();
sw.Start();
for (int i = 0; i < setSize; i++)
numbers[i].ToString();
sw.Stop();
std.Add(sw.ElapsedTicks);
}
Console.WriteLine();
Console.WriteLine("Running Time:");
Console.WriteLine("Iteration: {0} ({1} avg)",
TimeSpan.FromTicks(loop.Sum()),
TimeSpan.FromTicks((int)loop.Average()));
Console.WriteLine("Recursion: {0} ({1} avg)",
TimeSpan.FromTicks(recr.Sum()),
TimeSpan.FromTicks((int)recr.Average()));
Console.WriteLine("Standard : {0} ({1} avg)",
TimeSpan.FromTicks(std.Sum()),
TimeSpan.FromTicks((int)std.Average()));
double lSum = loop.Sum();
double rSum = recr.Sum();
double sSum = std.Sum();
Console.WriteLine();
Console.WriteLine("Ratios: \n" +
" | Iter | Rec | Std \n" +
"-----+------+------+-----");
foreach (var div in new[] { new {n = "Iter", t = lSum},
new {n = "Rec ", t = rSum},
new {n = "Std ", t = sSum}})
Console.WriteLine("{0} | {1:0.00} | {2:0.00} | {3:0.00}",
div.n, lSum / div.t, rSum / div.t, sSum / div.t);
Console.ReadLine();
}
String str = "" + a;会调用toString方法，我想这就是 @AMR 的意思。 - bizzehdee