go: add «1248. Count Number of Nice Subarrays»

Signed-off-by: Matej Focko <me@mfocko.xyz>

go/count-number-of-nice-subarrays.go

@@ -0,0 +1,23 @@
+package main
+
+func numberOfSubarrays(nums []int, k int) int {
+	atMost := func(k int) int {
+		subarrays := 0
+
+		window, start := 0, 0
+		for end := range nums {
+			window += nums[end] % 2
+
+			for window > k {
+				window -= nums[start] % 2
+				start++
+			}
+
+			subarrays += end - start + 1
+		}
+
+		return subarrays
+	}
+
+	return atMost(k) - atMost(k-1)
+}