Count occurrences of a substring: Difference between revisions
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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. |
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. |
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<lang pseudocode> |
<lang pseudocode>print countSubstring("the three truths","th") |
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3 |
3 |
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// do not count substrings that overlap with previously-counted substrings: |
// do not count substrings that overlap with previously-counted substrings: |
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print countSubstring("ababababab","abab") |
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⚫ | |||
2 |
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⚫ | |||
=={{header|Perl}}== |
=={{header|Perl}}== |
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print countSubstring("the three truths","th"), "\n"; |
print countSubstring("the three truths","th"), "\n"; |
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print countSubstring("ababababab","abab"), "\n"; |
print countSubstring("ababababab","abab"), "\n";</lang> |
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</lang> |
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=={{header|Python}}== |
=={{header|Python}}== |
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>>> "ababababab".count("abab") |
>>> "ababababab".count("abab") |
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2</lang> |
2</lang> |
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=={{header|Tcl}}== |
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The regular expression engine is ideal for matching this, especially as the <tt>***=</tt> prefix makes it interpret the rest of the argument as a literal string to match: |
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<lang tcl>proc countSubstrings {haystack needle} { |
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regexp -all ***=$needle $haystack |
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} |
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puts [countSubstrings "the three truths" "th"] |
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puts [countSubstrings "ababababab" "abab"]</lang> |
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Output:<pre>3 |
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2</pre> |
Revision as of 10:20, 16 June 2011
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You are encouraged to solve this task according to the task description, using any language you may know.
The task is to either create a function, or show a built-in function, to count the number of non-overlapping occurrences of a substring inside a string. The function should take two arguments: the first argument being the string to search and the second a substring to be search for. It should return an integer count.
<lang pseudocode>print countSubstring("the three truths","th") 3
// do not count substrings that overlap with previously-counted substrings: print countSubstring("ababababab","abab") 2</lang>
Perl
This solution uses regex, hence the substring cannot contain regex metacharacters <lang perl>sub countSubstring {
my ($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 matching this, 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"]</lang>
Output:
3 2