solution for find median from data stream - two heaps. rename filename for insertion sort solution

Author: emikhalev

leetcode/find_median_from_data_stream-solution-1-insertion-sort.go renamed to leetcode/find_median_from_data_stream-solution-2-insertion-sort.go

@@ -0,0 +1,138 @@
+// https://leetcode.com/problems/find-median-from-data-stream/
+
+package main
+
+type MedianFinder struct {
+	qLow, qHigh *PriorityQueue
+}
+
+/** initialize your data structure here. */
+func Constructor() MedianFinder {
+	return MedianFinder{
+		qLow:  NewQueue(func(i, j int) bool { return i > j }),
+		qHigh: NewQueue(func(i, j int) bool { return i < j }),
+	}
+}
+
+func (this *MedianFinder) AddNum(num int) {
+	this.qLow.Push(num)
+
+	v, _ := this.qLow.Top()
+	this.qHigh.Push(v)
+	this.qLow.Pop()
+
+	if this.qLow.Len() < this.qHigh.Len() {
+		v, _ := this.qHigh.Top()
+		this.qLow.Push(v)
+		this.qHigh.Pop()
+	}
+}
+
+func (this *MedianFinder) FindMedian() float64 {
+	if this.qLow.Len() > this.qHigh.Len() {
+		v, _ := this.qLow.Top()
+		return float64(v)
+	}
+	vl, _ := this.qLow.Top()
+	vh, _ := this.qHigh.Top()
+	return float64(vl+vh) / 2
+}
+
+type PriorityQueue struct {
+	compareFn func(i, j int) bool
+	data      []int
+}
+
+func NewQueue(compareFn func(i, j int) bool) *PriorityQueue {
+	return &PriorityQueue{
+		compareFn: compareFn,
+		data:      make([]int, 0),
+	}
+}
+
+func (q *PriorityQueue) Len() int {
+	return len(q.data)
+}
+
+func (q *PriorityQueue) Top() (int, bool) {
+	if len(q.data) > 0 {
+		return q.data[0], true
+	}
+	return 0, false
+}
+
+func (q *PriorityQueue) Push(num int) {
+	q.data = append(q.data, num)
+	q.siftUp()
+}
+
+func (q *PriorityQueue) Pop() (int, bool) {
+	if len(q.data) == 0 {
+		return 0, false
+	}
+
+	v := q.data[0]
+	q.data[0] = q.data[len(q.data)-1]
+	q.data = q.data[:len(q.data)-1]
+	q.siftDown()
+
+	return v, true
+}
+
+func (q *PriorityQueue) siftUp() {
+	cIdx := len(q.data) - 1 // current index
+	pIdx := (cIdx - 1) / 2
+
+	for cIdx > 0 && q.compareFn(q.data[cIdx], q.data[pIdx]) {
+		// xor swap (works for integers)
+		q.data[cIdx] = q.data[cIdx] ^ q.data[pIdx]
+		q.data[pIdx] = q.data[pIdx] ^ q.data[cIdx]
+		q.data[cIdx] = q.data[cIdx] ^ q.data[pIdx]
+
+		// update indexes
+		cIdx = pIdx
+		pIdx = (cIdx - 1) / 2
+	}
+}
+
+func (q *PriorityQueue) siftDown() {
+	if len(q.data) == 0 {
+		return
+	}
+
+	cIdx := 0
+	for {
+		// left and right indexes
+		lIdx := cIdx*2 + 1
+		rIdx := lIdx + 1
+
+		// find max
+		maxIdx := cIdx
+		if lIdx < len(q.data) && q.compareFn(q.data[lIdx], q.data[maxIdx]) {
+			maxIdx = lIdx
+		}
+		if rIdx < len(q.data) && q.compareFn(q.data[rIdx], q.data[maxIdx]) {
+			maxIdx = rIdx
+		}
+
+		// swap current with max
+		if cIdx == maxIdx {
+			break
+		}
+
+		// xor swap (works for integers)
+		q.data[cIdx] = q.data[cIdx] ^ q.data[maxIdx]
+		q.data[maxIdx] = q.data[maxIdx] ^ q.data[cIdx]
+		q.data[cIdx] = q.data[cIdx] ^ q.data[maxIdx]
+
+		// update current index
+		cIdx = maxIdx
+	}
+}
+
+/**
+ * Your MedianFinder object will be instantiated and called as such:
+ * obj := Constructor();
+ * obj.AddNum(num);
+ * param_2 := obj.FindMedian();
+ */