Count occurrences of a substring: Difference between revisions
m →[[Count_occurrences_of_a_substring#ALGOL 68]]: reduce # of test cases. |
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printf(($d" "$,
count string in string("
count string in string("
count string in string("
$l$
))</lang>
Output:
<pre>
</pre>
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Revision as of 12:44, 16 June 2011
![Task](http://static.miraheze.org/rosettacodewiki/thumb/b/ba/Rcode-button-task-crushed.png/64px-Rcode-button-task-crushed.png)
You are encouraged to solve this task according to the task description, using any language you may know.
The task is to either create a function, or show a built-in function, to count the number of non-overlapping occurrences of a substring inside a string. The function should take two arguments: the first argument being the string to search and the second a substring to be search for. It should return an integer count.
<lang pseudocode>print countSubstring("the three truths","th") 3
// do not count substrings that overlap with previously-counted substrings: print countSubstring("ababababab","abab") 2</lang>
ALGOL 68
Algol68 has no build in function to do this task, hence the next to create a count string in string routine. <lang algol68>#!/usr/local/bin/a68g --script #
PROC count string in string = (STRING needle, haystack)INT: (
INT start:=LWB haystack, next, out:=0; FOR count WHILE string in string(needle, next, haystack[start:]) DO start+:=next+UPB needle-LWB needle; out:=count OD; out
);
printf(($d" "$,
count string in string("th", "the three truths"), # expect 3 # count string in string("abab", "ababababab"), # expect 2 # count string in string("a*b", "abaabba*bbaba*bbab"), # expect 2 # $l$
))</lang> Output:
3 2 2
Perl
This solution uses regex, hence the substring cannot contain regex metacharacters <lang perl>sub countSubstring {
my ($str, $sub) = @_; my $count = () = $str =~ /$sub/g; return $count;
- or return scalar( () = $str =~ /$sub/g );
}
print countSubstring("the three truths","th"), "\n"; print countSubstring("ababababab","abab"), "\n";</lang>
Python
<lang python>>>> "the three truths".count("th") 3 >>> "ababababab".count("abab") 2</lang>
Tcl
The regular expression engine is ideal for this task, especially as the ***= prefix makes it interpret the rest of the argument as a literal string to match: <lang tcl>proc countSubstrings {haystack needle} {
regexp -all ***=$needle $haystack
} puts [countSubstrings "the three truths" "th"] puts [countSubstrings "ababababab" "abab"] puts [countSubstrings "abaabba*bbaba*bbab" "a*b"]</lang>
Output:
3 2 2