Question

I’m trying to diff two strings to determine whether or not they solely vary in one numerical subset of the string structure; for example,

varies_in_single_number_field('foo7bar', 'foo123bar') # Returns True, because 7 != 123, and there's only one varying # number region between the two strings. 

In Python I can use the difflib to accomplish this:

import difflib, doctest  def varies_in_single_number_field(str1, str2):     '''     A typical use case is as follows:         >>> varies_in_single_number_field('foo7bar00', 'foo123bar00')         True      Numerical variation in two dimensions is no good:         >>> varies_in_single_number_field('foo7bar00', 'foo123bar01')         False      Varying in a nonexistent field is okay:         >>> varies_in_single_number_field('foobar00', 'foo123bar00')         True      Identical strings don't *vary* in any number field:         >>> varies_in_single_number_field('foobar00', 'foobar00')         False     '''     in_differing_substring = False     passed_differing_substring = False # There should be only one.     differ = difflib.Differ()     for letter_diff in differ.compare(str1, str2):         letter = letter_diff[2:]         if letter_diff.startswith(('-', '+')):             if passed_differing_substring: # Already saw a varying field.                 return False             in_differing_substring = True             if not letter.isdigit(): return False # Non-digit diff character.         elif in_differing_substring: # Diff character not found - end of diff.             in_differing_substring = False             passed_differing_substring = True     return passed_differing_substring # No variation if no diff was passed.  if __name__ == '__main__': doctest.testmod() 

But I have no idea how to find something like difflib for C++. Alternative approaches welcome. 🙂

Answer 1

This might work, it at least passes your demonstration test: EDIT: I’ve made some modifications to deal with some string indexing issues. I believe it should be good now.

#include <iostream> #include <string> #include <vector> #include <algorithm> #include <cctype>  bool starts_with(const std::string &s1, const std::string &s2) {     return (s1.length() <= s2.length()) && (s2.substr(0, s1.length()) == s1); }  bool ends_with(const std::string &s1, const std::string &s2) {     return (s1.length() <= s2.length()) && (s2.substr(s2.length() - s1.length()) == s1); }  bool is_numeric(const std::string &s) {     for(std::string::const_iterator it = s.begin(); it != s.end(); ++it) {         if(!std::isdigit(*it)) {                 return false;         }     }     return true; }  bool varies_in_single_number_field(std::string s1, std::string s2) {      size_t index1 = 0;     size_t index2 = s1.length() - 1;      if(s1 == s2) {         return false;     }      if((s1.empty() && is_numeric(s2)) || (s2.empty() && is_numeric(s1))) {         return true;     }      if(s1.length() < s2.length()) {         s1.swap(s2);     }      while(index1 < s1.length() && starts_with(s1.substr(0, index1), s2)) { index1++; }     while(ends_with(s1.substr(index2), s2)) { index2--; }      return is_numeric(s1.substr(index1 - 1, (index2 + 1) - (index1 - 1)));  }  int main() {     std::cout << std::boolalpha << varies_in_single_number_field('foo7bar00', 'foo123bar00') << std::endl;     std::cout << std::boolalpha << varies_in_single_number_field('foo7bar00', 'foo123bar01') << std::endl;     std::cout << std::boolalpha << varies_in_single_number_field('foobar00', 'foo123bar00') << std::endl;     std::cout << std::boolalpha << varies_in_single_number_field('foobar00', 'foobar00') << std::endl;     std::cout << std::boolalpha << varies_in_single_number_field('7aaa', 'aaa') << std::endl;     std::cout << std::boolalpha << varies_in_single_number_field('aaa7', 'aaa') << std::endl;     std::cout << std::boolalpha << varies_in_single_number_field('aaa', '7aaa') << std::endl;     std::cout << std::boolalpha << varies_in_single_number_field('aaa', 'aaa7') << std::endl; } 

Basically, it looks for a string which has 3 parts, string2 begins with part1, string2 ends with part3 and part2 is only digits.