Design Pattern: 1. Sliding Window | Problem: Longest Substring with 'K' Distinct Characters

1_longest_substring_with_k_distinct_characters.cpp

@@ -0,0 +1,77 @@
+/*/ problem source:
+ * https://www.geeksforgeeks.org/find-the-longest-substring-with-k-unique-characters-in-a-given-string/
+ */
+#include <iostream>
+#include <ostream>
+#include <unordered_map>
+#include <vector>
+
+class result {
+public:
+  unsigned long longest_start = 0;
+  unsigned long longest_end = 0;
+  bool match_found = false;
+  bool operator==(const result r) {
+    return longest_start == r.longest_start && longest_end == r.longest_end &&
+           match_found == r.match_found;
+  };
+};
+
+struct input {
+  std::string s;
+  unsigned long k;
+};
+
+struct test_case {
+  input i;
+  result r;
+};
+
+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.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;
+}
+
+int main() {
+  std::vector<test_case> test_cases = {{{"aabacbebebe", 3}, {4, 10, true}},
+                                       {{"aabbcc", 1}, {0, 1, true}},
+                                       {{"aabbcc", 3}, {0, 5, true}},
+                                       {{"aaabbb", 3}, {0, 0, false}}};
+  for (const test_case &t : test_cases) {
+    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";
+    }
+  }
+  return 0;
+}

CMakeLists.txt

@@ -6,3 +6,5 @@ set(CMAKE_CXX_STANDARD 17)
 set(CMAKE_CXX_STANDARD_REQUIRED True)
 
 set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wall  -Wextra -Werror -g")
+
+add_executable(1_longest_substring_with_k_distinct_characters 1_longest_substring_with_k_distinct_characters.cpp)