feat: metamorphic test and partial verification

1_longest_substring_with_k_distinct_characters.cpp

@@ -4,12 +4,15 @@
  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> {
@@ -25,8 +28,8 @@ struct semicolon_is_space : std::ctype<char> {
 
 class input {
 public:
-  std::string s;
-  unsigned long k;
+  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);
 };
@@ -121,7 +124,34 @@ result find(const std::string &s, const unsigned long k) {
   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;
+}
+
 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]);
@@ -130,16 +160,43 @@ int main(int argc, char *argv[]) {
       test_case t;
       f >> t;
       if (t.i.s.length()) { // skip empty line/string inputs
-        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";
+        test(t);
+      }
+    }
+
+    std::cout
+        << "\n\n\nPerforming metamorphic tests from randomly generated input "
+           "(string and K values)"
+        << 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 < 1; i++) {
+      test_case t;
+      t.i.s += (char)random_ascii_char();
+      std::cout << t;
+      t.r = find(t.i.s, t.i.k);
+      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();
+          std::cout << t;
+          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;
+          assert(K_verify(t));
+        }
+        while (t.r.match_found) {
+          std::cout << t;
+          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;
+          assert(K_verify(t));
         }
-        std::cout << "\n";
+        t.i.k = rng(1, --t.i.k);
       }
     }
   }