Feat: 295. Find Median from Data Stream

Author: HC-kang

find-median-from-data-stream/HC-kang.ts

@@ -0,0 +1,164 @@
+/**
+ * https://leetcode.com/problems/find-median-from-data-stream
+ * array with binary search
+ */
+class MedianFinder {
+  // S.C. O(n)
+  private nums: number[] = [];
+
+  // T.C. O(n)
+  addNum(num: number): void {
+    if (this.nums.length === 0) {
+      this.nums.push(num);
+      return;
+    } else {
+      this.putNumWithBinarySearch(num);
+    }
+  }
+
+  private putNumWithBinarySearch(num: number): void {
+    let left = 0;
+    let right = this.nums.length - 1;
+
+    while (left <= right) {
+      const mid = Math.floor((left + right) / 2);
+      if (this.nums[mid] === num) {
+        this.nums.splice(mid, 0, num);
+        return;
+      } else if (this.nums[mid] < num) {
+        left = mid + 1;
+      } else {
+        right = mid - 1;
+      }
+    }
+
+    // T.C. O(n)
+    this.nums.splice(left, 0, num);
+  }
+
+  // T.C. O(1)
+  findMedian(): number {
+    const len = this.nums.length;
+
+    if (len % 2 === 1) {
+      return this.nums[Math.floor(len / 2)];
+    } else {
+      return (this.nums[len / 2] + this.nums[len / 2 - 1]) / 2;
+    }
+  }
+}
+
+/**
+ * heap...
+ * TL;DR
+ */
+class MedianFinder {
+  // S.C. O(n)
+  private smallHalf: MaxHeap = new MaxHeap();
+  private largeHalf: MinHeap = new MinHeap();
+
+  // T.C. O(log n)
+  addNum(num: number): void {
+    this.smallHalf.push(num);
+    this.largeHalf.push(this.smallHalf.pop()!);
+
+    if (this.smallHalf.size() < this.largeHalf.size()) {
+      this.smallHalf.push(this.largeHalf.pop()!);
+    }
+  }
+
+  // T.C. O(1)
+  findMedian(): number {
+    if (this.smallHalf.size() === this.largeHalf.size()) {
+      return (this.smallHalf.peek()! + this.largeHalf.peek()!) / 2;
+    } else {
+      return this.smallHalf.peek()!;
+    }
+  }
+}
+
+class MinHeap {
+  protected heap: number[] = [];
+
+  push(val: number): void {
+    this.heap.push(val);
+    this.heapifyUp();
+  }
+
+  pop(): number | undefined {
+    if (this.heap.length === 0) return undefined;
+    if (this.heap.length === 1) return this.heap.pop();
+
+    const result = this.heap[0];
+    this.heap[0] = this.heap.pop()!;
+    this.heapifyDown();
+    return result;
+  }
+
+  peek(): number | undefined {
+    return this.heap[0];
+  }
+
+  size(): number {
+    return this.heap.length;
+  }
+
+  private heapifyUp(): void {
+    let index = this.heap.length - 1;
+    while (index > 0) {
+      const parentIndex = Math.floor((index - 1) / 2);
+      if (this.heap[parentIndex] <= this.heap[index]) break;
+
+      this.swap(parentIndex, index);
+      index = parentIndex;
+    }
+  }
+
+  private heapifyDown(): void {
+    let index = 0;
+    while (true) {
+      let smallest = index;
+      const leftChild = 2 * index + 1;
+      const rightChild = 2 * index + 2;
+
+      if (
+        leftChild < this.heap.length &&
+        this.heap[leftChild] < this.heap[smallest]
+      ) {
+        smallest = leftChild;
+      }
+
+      if (
+        rightChild < this.heap.length &&
+        this.heap[rightChild] < this.heap[smallest]
+      ) {
+        smallest = rightChild;
+      }
+
+      if (smallest === index) break;
+
+      this.swap(index, smallest);
+      index = smallest;
+    }
+  }
+
+  protected swap(i: number, j: number): void {
+    [this.heap[i], this.heap[j]] = [this.heap[j], this.heap[i]];
+  }
+}
+
+class MaxHeap extends MinHeap {
+  push(val: number): void {
+    super.push(-val);
+  }
+
+  pop(): number | undefined {
+    const val = super.pop();
+    return val === undefined ? undefined : -val;
+  }
+
+  peek(): number | undefined {
+    const val = super.peek();
+    return val === undefined ? undefined : -val;
+  }
+}