How to speed up this Clojure code? - regex

Question

I am a beginner in clojure. I am trying to solve this simple problem on codechef using clojure. Below is my clojure code but this code is taking too long to run and gives TimeoutException. Can someone please help me to optimize this code and make it run faster.
(defn checkCase [str]
(let [len (count str)]
(and (> len 1) (re-matches #"[A-Z]+" str))))
(println (count (filter checkCase (.split (read-line) " "))))
Note: My program is not getting timedout due to input error. On codechef input is handled automatically (probably through input redirection. Please read the question for more details)
Thank you!

Answer 1

Most text finding exercises are exercizes in regexps, this one no different. It's usually pretty hard to find a more efficient way in whatever programming language that will outpace good regexp implementations.
In this case re-seq, look around regexps, repetition limiting and the multiline regexp flag (?m) are your friends
(defn find-acronyms
[s]
(re-seq #"(?m)(?<=\W|^)[A-Z]+(?=\W|$)" s))
(find-acronyms "I like coding and will participate in IOI Then there is ICPC")
=> ("IOI" "ICPC")
Let's dissect the regex:
(?m) The multiline flag: lets you match your regex over multiple lines, so no need to split into multiple strings
(?<=\W|^) The match should follow a non-word character or the beginning of the (multiline) string
[A-Z]{2,} Match concurrent capital letters, a minimum of 2
(?=\W|$) The match should be followed by a non-word character or the end of the (multiline) string

Answer 2

I can only guess that wherever you run this snippet of code, it doesn't feed anything to your read-line invocation. Or maybe it does, but doesn't send a newline as the last thing. So it hangs waiting.

Answer 3

(defn checkCase [str]
(let [len (count str)]
(and (> len 1) (re-matches #"[A-Z]+" str))))
(defn answer [str]
(println (count (filter checkCase (.split str " ")))))
So at the REPL:
=> (answer "GGG fff TTT")
;-> 2
;-> nil
The answer is being printed to the screen. But probably best to have your function return the answer rather than print it out:
(defn answer [str]
(count (filter checkCase (.split str " "))))
All I have done is replaced your (read-line) with an argument. (read-line) is expecting input from stdin and waiting for it forever - or until a timeout happens in your case.

Answer 4

I am not sure if this is the slow part of your code, but if it is your could try to split up the execution and safe gard the very slow regexp part by executing it when it is necessary. I think the current version with AND already does that. If it does not you can try to do something else, like this:
(defn checkCase [^String str]
(cond
(< (.length str) 2)
false
(re-matches #"[A-Z]+" str)
true
:else
false))

Answer 5

maybe you could try using re-seq instead of spltting the string and checking every item? So you will lose the filter, .split, and additional function call. Something like this:
(println (count (re-seq #"\b[A-Z]{2,}?\b" (read-line))))

Answer 6

You need to submit a Java program. You can test it on the command line before you submit it. You can but don't need to use redirection symbols (<,>). Just type the input and see that every time you do it returns the count after you have typed enter.
You will need aot compilation (Ahead Of Time, which means that .class files are included) and a main that is exported. Only then will it become a Java program.
Actually when they ask for a Java program they probably mean a .class file. You can run a .class file with the java program (which I imagine is what their test-runner does). Put it in a shell or batch file when testing, but just submit the .class file.