add Find Median from Data Stream solution

Author: HoonDongKang

find-median-from-data-stream/HoonDongKang.ts

@@ -0,0 +1,127 @@
+/**
+ * [Problem]: [295] Find Median from Data Stream
+ * (https://leetcode.com/problems/find-median-from-data-stream/description/)
+ */
+class Heap {
+    private numbers: number[];
+    private compare: (a: number, b: number) => boolean;
+
+    constructor(compare: (a: number, b: number) => boolean) {
+        this.numbers = [];
+        this.compare = compare;
+    }
+
+    private getParentIdx(index: number) {
+        return Math.floor((index - 1) / 2);
+    }
+
+    private getLeftChildIdx(index: number) {
+        return 2 * index + 1;
+    }
+
+    private getRightChildIdx(index: number) {
+        return 2 * index + 2;
+    }
+
+    private swap(index1: number, index2: number): void {
+        [this.numbers[index1], this.numbers[index2]] = [this.numbers[index2], this.numbers[index1]];
+    }
+
+    private heapifyUp(index: number) {
+        const parentIndex = this.getParentIdx(index);
+        if (0 <= parentIndex && this.compare(this.numbers[index], this.numbers[parentIndex])) {
+            this.swap(index, parentIndex);
+            this.heapifyUp(parentIndex);
+        }
+    }
+
+    private heapifyDown(index: number): void {
+        const leftChildIndex = this.getLeftChildIdx(index);
+        const rightChildIndex = this.getRightChildIdx(index);
+        let largestIndex = index;
+
+        if (
+            leftChildIndex < this.numbers.length &&
+            this.compare(this.numbers[leftChildIndex], this.numbers[largestIndex])
+        ) {
+            largestIndex = leftChildIndex;
+        }
+
+        if (
+            rightChildIndex < this.numbers.length &&
+            this.compare(this.numbers[rightChildIndex], this.numbers[largestIndex])
+        ) {
+            largestIndex = rightChildIndex;
+        }
+
+        if (largestIndex !== index) {
+            this.swap(index, largestIndex);
+            this.heapifyDown(largestIndex);
+        }
+    }
+
+    insert(number: number) {
+        this.numbers.push(number);
+        this.heapifyUp(this.numbers.length - 1);
+    }
+
+    pop() {
+        if (this.numbers.length === 0) {
+            return null;
+        }
+
+        if (this.numbers.length === 1) {
+            return this.numbers.pop()!;
+        }
+
+        const root = this.numbers[0];
+        this.numbers[0] = this.numbers.pop()!;
+        this.heapifyDown(0);
+
+        return root;
+    }
+
+    peek() {
+        return this.numbers.length > 0 ? this.numbers[0] : null;
+    }
+
+    size(): number {
+        return this.numbers.length;
+    }
+}
+
+class MedianFinder {
+    private smallHeap: Heap;
+    private largeHeap: Heap;
+
+    constructor() {
+        this.smallHeap = new Heap((a, b) => a > b);
+        this.largeHeap = new Heap((a, b) => a < b);
+    }
+
+    //시간복잡도 O(log n)
+    addNum(num: number): void {
+        this.smallHeap.insert(num);
+        this.largeHeap.insert(this.smallHeap.pop()!);
+
+        if (this.smallHeap.size() < this.largeHeap.size()) {
+            this.smallHeap.insert(this.largeHeap.pop()!);
+        }
+    }
+
+    //시간복잡도 O(1)
+    findMedian(): number {
+        if (this.smallHeap.size() > this.largeHeap.size()) {
+            return this.smallHeap.peek()!;
+        } else {
+            return (this.smallHeap.peek()! + this.largeHeap.peek()!) / 2;
+        }
+    }
+}
+
+/**
+ * Your MedianFinder object will be instantiated and called as such:
+ * var obj = new MedianFinder()
+ * obj.addNum(num)
+ * var param_2 = obj.findMedian()
+ */