[tedkimdev] WEEK 13 Solutions

find-median-from-data-stream/tedkimdev.go

@@ -0,0 +1,82 @@
+type MedianFinder struct {
+	small *MaxHeap // lower half
+	large *MinHeap // upper half
+}
+
+func Constructor() MedianFinder {
+	small := &MaxHeap{}
+	large := &MinHeap{}
+	heap.Init(small)
+	heap.Init(large)
+
+	return MedianFinder{
+		small: small,
+		large: large,
+	}
+}
+
+// SC: O(n)
+// TC: O(m * log n)
+func (this *MedianFinder) AddNum(num int) {
+	if this.small.Len() == 0 || num <= (*this.small)[0] {
+		heap.Push(this.small, num)
+	} else {
+		heap.Push(this.large, num)
+	}
+
+	// rebalance
+	if this.small.Len() > this.large.Len()+1 {
+		v := heap.Pop(this.small).(int)
+		heap.Push(this.large, v)
+	}
+
+	if this.large.Len() > this.small.Len() {
+		v := heap.Pop(this.large).(int)
+		heap.Push(this.small, v)
+	}
+}
+
+// TC: O(m)
+func (this *MedianFinder) FindMedian() float64 {
+	if this.small.Len() > this.large.Len() {
+		return float64((*this.small)[0])
+	}
+
+	return float64((*this.small)[0]+(*this.large)[0]) / 2.0
+}
+
+type MinHeap []int
+
+func (h MinHeap) Len() int           { return len(h) }
+func (h MinHeap) Less(i, j int) bool { return h[i] < h[j] }
+func (h MinHeap) Swap(i, j int)      { h[i], h[j] = h[j], h[i] }
+
+func (h *MinHeap) Push(x interface{}) {
+	*h = append(*h, x.(int))
+}
+
+func (h *MinHeap) Pop() interface{} {
+	old := *h
+	n := len(old)
+	x := old[n-1]
+	*h = old[:n-1]
+	return x
+}
+
+type MaxHeap []int
+
+func (h MaxHeap) Len() int           { return len(h) }
+func (h MaxHeap) Less(i, j int) bool { return h[i] > h[j] } // reverse
+func (h MaxHeap) Swap(i, j int)      { h[i], h[j] = h[j], h[i] }
+
+func (h *MaxHeap) Push(x interface{}) {
+	*h = append(*h, x.(int))
+}
+
+func (h *MaxHeap) Pop() interface{} {
+	old := *h
+	n := len(old)
+	x := old[n-1]
+	*h = old[:n-1]
+	return x
+}