feat(soobing): week13 > find-median-from-data-stream

Author: soobing

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

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+/**
+ * 문제 설명
+ * - 중간 값을 찾는 문제
+ *
+ * 아이디어 (👀 어려움..)
+ * - 최대 힙과 최소 힙을 사용하여 중간 값을 찾는다.
+ */
+class MinHeap {
+  heap: number[] = [];
+  size(): number {
+    return this.heap.length;
+  }
+  peek(): number | null {
+    return this.heap[0] ?? null;
+  }
+  push(val: number) {
+    this.heap.push(val);
+    this.bubbleUp(this.size() - 1);
+  }
+  pop(): number | null {
+    if (this.size() === 0) return null;
+    const top = this.heap[0];
+    const end = this.heap.pop()!;
+    if (this.size() > 0) {
+      this.heap[0] = end;
+      this.bubbleDown(0);
+    }
+    return top;
+  }
+  private bubbleUp(idx: number) {
+    while (idx > 0) {
+      const parent = Math.floor((idx - 1) / 2);
+      if (this.heap[parent] <= this.heap[idx]) break;
+      [this.heap[parent], this.heap[idx]] = [this.heap[idx], this.heap[parent]];
+      idx = parent;
+    }
+  }
+  private bubbleDown(idx: number) {
+    const n = this.size();
+    while (true) {
+      let left = idx * 2 + 1;
+      let right = idx * 2 + 2;
+      let smallest = idx;
+      if (left < n && this.heap[left] < this.heap[smallest]) smallest = left;
+      if (right < n && this.heap[right] < this.heap[smallest]) smallest = right;
+      if (smallest === idx) break;
+      [this.heap[smallest], this.heap[idx]] = [
+        this.heap[idx],
+        this.heap[smallest],
+      ];
+      idx = smallest;
+    }
+  }
+}
+
+class MaxHeap {
+  heap: number[] = [];
+  size(): number {
+    return this.heap.length;
+  }
+  peek(): number | null {
+    return this.heap[0] ?? null;
+  }
+  push(val: number) {
+    this.heap.push(val);
+    this.bubbleUp(this.size() - 1);
+  }
+  pop(): number | null {
+    if (this.size() === 0) return null;
+    const top = this.heap[0];
+    const end = this.heap.pop()!;
+    if (this.size() > 0) {
+      this.heap[0] = end;
+      this.bubbleDown(0);
+    }
+    return top;
+  }
+  private bubbleUp(idx: number) {
+    while (idx > 0) {
+      const parent = Math.floor((idx - 1) / 2);
+      if (this.heap[parent] >= this.heap[idx]) break;
+      [this.heap[parent], this.heap[idx]] = [this.heap[idx], this.heap[parent]];
+      idx = parent;
+    }
+  }
+  private bubbleDown(idx: number) {
+    const n = this.size();
+    while (true) {
+      let left = idx * 2 + 1;
+      let right = idx * 2 + 2;
+      let largest = idx;
+      if (left < n && this.heap[left] > this.heap[largest]) largest = left;
+      if (right < n && this.heap[right] > this.heap[largest]) largest = right;
+      if (largest === idx) break;
+      [this.heap[largest], this.heap[idx]] = [
+        this.heap[idx],
+        this.heap[largest],
+      ];
+      idx = largest;
+    }
+  }
+}
+
+class MedianFinder {
+  private minH = new MinHeap();
+  private maxH = new MaxHeap();
+
+  addNum(num: number): void {
+    if (this.maxH.size() === 0 || num <= (this.maxH.peek() ?? num)) {
+      this.maxH.push(num);
+    } else {
+      this.minH.push(num);
+    }
+
+    // Rebalance
+    if (this.maxH.size() > this.minH.size() + 1) {
+      this.minH.push(this.maxH.pop()!);
+    } else if (this.minH.size() > this.maxH.size()) {
+      this.maxH.push(this.minH.pop()!);
+    }
+  }
+
+  findMedian(): number {
+    const total = this.maxH.size() + this.minH.size();
+    if (total % 2 === 1) {
+      return this.maxH.peek()!;
+    } else {
+      return (this.maxH.peek()! + this.minH.peek()!) / 2;
+    }
+  }
+}