Design Pattern 10: Two Heaps: Problem: Find Median from Data Stream

10_find_the_median_of_a_number_stream.cpp

@@ -0,0 +1,82 @@
+/* Problem: https://leetcode.com/problems/find-median-from-data-stream/
+ */
+
+#include <algorithm>
+#include <functional>
+#include <iostream>
+#include <limits>
+#include <queue>
+#include <vector>
+
+enum class action { addNum, findMedian };
+
+struct instruction {
+  action do_;
+  double val;
+};
+class MedianFinder {
+private:
+  std::priority_queue<double, std::vector<double>, std::greater<double>>
+      min_heap{std::greater<double>{}, {std::numeric_limits<double>::max()}};
+  std::priority_queue<double> max_heap{std::less<double>{},
+                                       {std::numeric_limits<double>::lowest()}};
+
+public:
+  MedianFinder() {}
+
+  void addNum(double num) {
+    if (min_heap.size() == max_heap.size()) {
+      if (num > min_heap.top()) {
+        min_heap.push(num);
+      } else {
+        max_heap.push(num);
+      }
+    } else if (min_heap.size() < max_heap.size()) {
+      if (num > max_heap.top()) {
+        min_heap.push(num);
+      } else {
+        min_heap.push(max_heap.top());
+        max_heap.pop();
+        max_heap.push(num);
+      }
+    } else {
+      if (num > min_heap.top()) {
+        max_heap.push(min_heap.top());
+        min_heap.pop();
+        min_heap.push(num);
+      } else {
+        max_heap.push(num);
+      }
+    }
+  }
+
+  double findMedian() {
+    if (min_heap.size() == max_heap.size()) {
+      return (min_heap.top() + max_heap.top()) / 2;
+    } else if (min_heap.size() < max_heap.size()) {
+      return max_heap.top();
+    } else {
+      return min_heap.top();
+    }
+  }
+};
+
+int main() {
+  std::vector<instruction> instructions = {{action::addNum, 1},
+                                           {action::addNum, 2},
+                                           {action::findMedian, 0},
+                                           {action::addNum, 3},
+                                           {action::findMedian, 0}};
+  MedianFinder *median_finder = new MedianFinder();
+  std::cout << "{";
+  for (instruction &i : instructions) {
+    if (i.do_ == action::addNum) {
+      median_finder->addNum(i.val);
+      std::cout << "null, ";
+    } else if (i.do_ == action::findMedian) {
+      i.val = median_finder->findMedian();
+      std::cout << i.val << ", ";
+    }
+  }
+  std::cout << "\b\b}\n";
+}

CMakeLists.txt

@@ -22,3 +22,5 @@ add_executable(7_reverse_nodes_in_k_group 7_reverse_nodes_in_k_group.cpp)
 add_executable(8_binary_tree_level_order_traversal 8_binary_tree_level_order_traversal.cpp)
 
 add_executable(9_path_sum_iii 9_path_sum_iii.cpp)
+
+add_executable(10_find_the_median_of_a_number_stream 10_find_the_median_of_a_number_stream.cpp)