find median from data stream

Author: eunhwa99

find-median-from-data-stream/eunhwa99.kt

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+import java.util.PriorityQueue
+class MedianFinder() {
+    // 1 2 3 4 5
+    // 중간값을 기준으로 
+    //   3
+    //  2 4
+    // 1   5
+    // 1 2 : maxHeap
+    // 4 5 : minHeap
+    private val maxHeap = PriorityQueue<Int> { a, b -> b - a }
+    private val minHeap = PriorityQueue<Int>()
+
+    // TC: O(log n)
+    // SC: O(n)
+    fun addNum(num: Int) {
+       if(maxHeap.isEmpty() || maxHeap.peek() >= num) {
+        maxHeap.add(num)
+       } else {
+        minHeap.add(num)
+       }
+
+       if(maxHeap.size > minHeap.size + 1) {
+        minHeap.add(maxHeap.poll())
+       } else if(minHeap.size > maxHeap.size) {
+        maxHeap.add(minHeap.poll())
+       }
+    }
+
+    fun findMedian(): Double {
+       if(maxHeap.size == minHeap.size) {
+        return (maxHeap.peek() + minHeap.peek()) / 2.0
+       } else {
+        return maxHeap.peek().toDouble()
+       }
+    }
+
+}