solve 295.find-median-from-data-stream

Author: andavid

vscode/295.find-median-from-data-stream.java

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+/*
+ * @lc app=leetcode id=295 lang=java
+ *
+ * [295] Find Median from Data Stream
+ *
+ * https://leetcode.com/problems/find-median-from-data-stream/description/
+ *
+ * algorithms
+ * Hard (34.96%)
+ * Total Accepted:    101.2K
+ * Total Submissions: 282.3K
+ * Testcase Example:  '["MedianFinder","addNum","addNum","findMedian","addNum","findMedian"]\n[[],[1],[2],[],[3],[]]'
+ *
+ * Median is the middle value in an ordered integer list. If the size of the
+ * list is even, there is no middle value. So the median is the mean of the two
+ * middle value.
+ * For example,
+ *
+ * [2,3,4], the median is 3
+ *
+ * [2,3], the median is (2 + 3) / 2 = 2.5
+ *
+ * Design a data structure that supports the following two operations:
+ *
+ *
+ * void addNum(int num) - Add a integer number from the data stream to the data
+ * structure.
+ * double findMedian() - Return the median of all elements so far.
+ *
+ *
+ *
+ *
+ * Example:
+ *
+ *
+ * addNum(1)
+ * addNum(2)
+ * findMedian() -> 1.5
+ * addNum(3)
+ * findMedian() -> 2
+ *
+ *
+ *
+ *
+ * Follow up:
+ *
+ *
+ * If all integer numbers from the stream are between 0 and 100, how would you
+ * optimize it?
+ * If 99% of all integer numbers from the stream are between 0 and 100, how
+ * would you optimize it?
+ *
+ *
+ */
+class MedianFinder {
+
+  public PriorityQueue<Integer> minheap, maxheap;
+
+  /** initialize your data structure here. */
+  public MedianFinder() {
+    minheap = new PriorityQueue<Integer>();
+    maxheap = new PriorityQueue<Integer>(Collections.reverseOrder());
+  }
+
+  public void addNum(int num) {
+    maxheap.add(num);
+    minheap.add(maxheap.poll());
+    if (maxheap.size() < minheap.size()) {
+      maxheap.add(minheap.poll());
+    }
+  }
+
+  public double findMedian() {
+    if (minheap.size() == maxheap.size()) {
+      return (minheap.peek() + maxheap.peek()) * 0.5;
+    } else {
+      return maxheap.peek();
+    }
+  }
+}
+
+/**
+ * Your MedianFinder object will be instantiated and called as such:
+ * MedianFinder obj = new MedianFinder();
+ * obj.addNum(num);
+ * double param_2 = obj.findMedian();
+ */
+