[Neetcode] Top K Frequent Elements

Author: GauthamBanasandra

Neetcode/CMakeLists.txt

@@ -1,7 +1,8 @@
 cmake_minimum_required(VERSION 3.12)
 project(Neetcode)
 
-set(CMAKE_CXX_STANDARD 20)
+set(CMAKE_CXX_STANDARD 17)
 
 add_executable(Two_sum_neetcode "Two sum/Two sum.cpp")
 add_executable(Group_anagrams_neetcode "Group anagrams/Group anagrams.cpp")
+add_executable(Top_K_Frequent_Elements "Top K Frequent Elements/Top K Frequent Elements.cpp")

Neetcode/Top K Frequent Elements/Top K Frequent Elements.cpp

@@ -0,0 +1,48 @@
+#include <algorithm>
+#include <iostream>
+#include <limits>
+#include <optional>
+#include <unordered_map>
+#include <vector>
+
+class Solution {
+public:
+  std::vector<int> topKFrequent(std::vector<int> &nums, int k);
+};
+
+std::vector<int> Solution::topKFrequent(std::vector<int> &nums, int k) {
+  std::unordered_map<int, std::size_t> freq_table;
+  for (const auto num : nums) {
+    ++freq_table[num];
+  }
+
+  std::vector<std::vector<int>> freq_order(nums.size() + 1);
+  for (const auto &kv : freq_table) {
+    const auto &value = kv.first;
+    const auto &freq = kv.second;
+    freq_order[freq].emplace_back(value);
+  }
+
+  std::vector<int> k_freq;
+  k_freq.reserve(k);
+  for (auto i_it = freq_order.rbegin(); i_it != freq_order.rend(); ++i_it) {
+    if (i_it->empty()) {
+      continue;
+    }
+
+    for (auto j_it = i_it->begin(); j_it != i_it->end() && k > 0; ++j_it, --k) {
+      k_freq.emplace_back(*j_it);
+    }
+  }
+  return k_freq;
+}
+
+int main(int argc, char *argv[]) {
+  std::vector nums{1, 2, 2, 3, 3, 3};
+  auto k = 2;
+  for (const auto num : Solution().topKFrequent(nums, k)) {
+    std::cout << num << std::endl;
+  }
+
+  return 0;
+}