您将如何计算字符串中字符串(实际上是字符)的出现次数? [英] How would you count occurrences of a string (actually a char) within a string?

问题描述

I am doing something where I realised I wanted to count how many /s I could find in a string, and then it struck me, that there were several ways to do it, but couldn't decide on what the best (or easiest) was.

At the moment I'm going with something like:

string source = "/once/upon/a/time/";
int count = source.Length - source.Replace("/", "").Length;

But I don't like it at all, any takers?

I don't really want to dig out RegEx for this, do I?

I know my string is going to have the term I'm searching for, so you can assume that...

Of course for strings where length > 1,

string haystack = "/once/upon/a/time";
string needle = "/";
int needleCount = ( haystack.Length - haystack.Replace(needle,"").Length ) / needle.Length;

解决方案

If you're using .NET 3.5 you can do this in a one-liner with LINQ:

int count = source.Count(f => f == '/');

If you don't want to use LINQ you can do it with:

int count = source.Split('/').Length - 1;

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You might be surprised to learn that your original technique seems to be about 30% faster than either of these! I've just done a quick benchmark with "/once/upon/a/time/" and the results are as follows:

Your original = 12s
source.Count = 19s
source.Split = 17s
foreach (from bobwienholt's answer) = 10s

(The times are for 50,000,000 iterations so you're unlikely to notice much difference in the real world.)

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