20-Coding-Patterns-DesignGurus.org/1_longest_substring_with_k_distinct_characters.cpp

/*/ problem source:
 * https://www.geeksforgeeks.org/find-the-longest-substring-with-k-unique-characters-in-a-given-string/

 Possible references include:
https://stackoverflow.com/a/7304184 - custom delimeter for istream
 */
#include "lib_random.h"
#include <cassert>
#include <fstream>
#include <iostream>
#include <locale>
#include <sstream>
#include <string>
#include <unordered_map>
#include <unordered_set>
#include <vector>

struct semicolon_is_space : std::ctype<char> {
  // this struct/class is adapted from: https://stackoverflow.com/a/7304184
  semicolon_is_space() : std::ctype<char>(get_table()){};
  static mask const *get_table() {
    static mask rc[table_size];
    rc[(int)';'] = std::ctype_base::space;
    rc[(int)'\n'] = std::ctype_base::space;
    return &rc[0];
  };
};

class input {
public:
  std::string s = "";
  unsigned long k = 1;
  friend std::istream &operator>>(std::istream &in, input &i);
  friend std::ostream &operator<<(std::ostream &out, const input &i);
};

std::istream &operator>>(std::istream &in, input &i) {
  in >> i.s >> i.k;
  return in;
}

std::ostream &operator<<(std::ostream &out, const input &i) {
  out << "String:\n" << i.s << "\nK: " << i.k << std::endl;
  return out;
}

class result {
public:
  unsigned long longest_start = 0;
  unsigned long longest_end = 0;
  bool match_found = false;
  bool operator==(const result r) const;
  friend std::istream &operator>>(std::istream &in, result &r);
  friend std::ostream &operator<<(std::ostream &out, const result &r);
};

bool result::operator==(const result r) const {
  return longest_start == r.longest_start && longest_end == r.longest_end &&
         match_found == r.match_found;
}

std::istream &operator>>(std::istream &in, result &r) {
  in >> r.longest_start >> r.longest_end >> r.match_found;
  return in;
}

std::ostream &operator<<(std::ostream &out, const result &r) {
  out << "longest_start: " << r.longest_start
      << " longest_end: " << r.longest_end << " match_found: ";
  if (r.match_found)
    out << "true";
  else
    out << "false";
  out << std::endl;
  return out;
}

class test_case {
public:
  input i;
  result r;
  friend std::istream &operator>>(std::istream &in, test_case &t);
  friend std::ostream &operator<<(std::ostream &out, const test_case &t);
};

std::istream &operator>>(std::istream &in, test_case &t) {
  in >> t.i >> t.r;
  return in;
}

std::ostream &operator<<(std::ostream &out, const test_case &t) {
  out << t.i << t.r;
  return out;
}

result find(const std::string &s, const unsigned long k) {
  result r;
  std::unordered_map<char, unsigned long> char_count;
  unsigned long start = 0, end = 0;
  for (; end < s.length(); end++) {
    char_count[s[end]] += 1;
    while (char_count.size() > k) {
      char_count[s[start]]--;
      if (char_count[s[start]] == 0) {
        char_count.erase(s[start]);
      }
      start++;
    }
    if (char_count.size() == k &&
        (end - start > r.longest_end - r.longest_start ||
         r.match_found == false)) {
      r.longest_start = start, r.longest_end = end;
      r.match_found = true;
    }
  }

  if (r.match_found) {
    std::cout << "Longest substring is \""
              << s.substr(r.longest_start, r.longest_end - r.longest_start + 1)
              << "\" with length " << r.longest_end - r.longest_start + 1
              << ".\n";
  } else {
    std::cout << "Could not find any match, not enough unique characters.\n";
  }
  return r;
}

void test(const test_case &t) {
  std::cout << t;
  if (find(t.i.s, t.i.k) == t.r) {
    std::cout << "Test case with string \"" << t.i.s << "\" and k=" << t.i.k
              << " passed.\n";
  } else {
    std::cout << std::flush;
    std::cerr << "TEST CASE WITH STRING \"" << t.i.s << "\" AND k=" << t.i.k
              << " FAILED.\n";
  }
  std::cout << "\n";
}

bool K_verify(const test_case &t) {
  // Verifies if found solution has exactly K unique characters (one of the
  // problem requirement)
  if (!t.r.match_found)
    return true; // Do not check if no match found
  std::unordered_set<char> unique_chars;
  for (const char c : t.i.s.substr(t.r.longest_start,
                                   t.r.longest_end - t.r.longest_start + 1)) {
    unique_chars.insert(c);
  }
  return unique_chars.size() == t.i.k;
}

bool thorough_test(const test_case &t) {
  unsigned long org_window_size = t.r.longest_end - t.r.longest_start + 1;
  if (org_window_size >= t.i.s.length())
    return true;
  for (unsigned long i = 0, n_tests = t.i.s.length() - org_window_size;
       i < n_tests; i++) {
    result r = {i, i + org_window_size, true};
    test_case mock_test = {t.i, r};
    if (K_verify(mock_test))
      return false;
  }
  return true;
}

int main(int argc, char *argv[]) {
  std::cout << "Processing static test cases from input file (if any)\n";
  semicolon_is_space delimeter;
  for (int i = 1; i < argc; i++) {
    std::ifstream f(argv[i]);
    f.imbue(std::locale(f.getloc(), new semicolon_is_space));
    while (f.good()) {
      test_case t;
      f >> t;
      if (t.i.s.length()) { // skip empty line/string inputs
        test(t);
      }
    }
  }

  // Thorough test (100% verifiable correct) is performaned randomly in ~1%
  // cases
  std::cout << "\n\n\nPerforming metamorphic tests from randomly generated "
               "input (string and K values).\nThorough test (100\% verifiable "
               "correct) is performaned randomly in ~1\% cases."
            << std::endl;
  random_number_generator<unsigned int> random_ascii_char(97, 122); // a-z
  random_number_generator<unsigned int> rng;
  for (unsigned int i = 0; i < 10; i++) {
    test_case t;
    t.i.s += (char)random_ascii_char();
    t.r = find(t.i.s, t.i.k);
    std::cout << t;
    for (unsigned int j = 0; j < 10; j++) {
      for (unsigned int k = 0, increase_str_len_by = rng(100, 1000);
           k < increase_str_len_by; k++) {
        t.i.s += (char)random_ascii_char();
        result r = find(t.i.s, t.i.k);
        if (r.match_found && t.r.match_found)
          assert(r.longest_end - r.longest_start >=
                 t.r.longest_end - t.r.longest_start);
        t.r = r;
        std::cout << t;
        assert(K_verify(t));
        if (!rng(0, 99))
          assert(thorough_test(t));
      }
      while (t.r.match_found) {
        result r = find(t.i.s, ++t.i.k);
        if (r.match_found)
          assert(r.longest_end - r.longest_start >=
                 t.r.longest_end - t.r.longest_start);
        t.r = r;
        std::cout << t;
        assert(K_verify(t));
        if (!rng(0, 99))
          assert(thorough_test(t));
      }
      t.i.k = rng(1, --t.i.k);
    }
  }
  return 0;
}