go: add «2176. Count Equal and Divisible Pairs in an Array»

URL:	https://leetcode.com/problems/count-equal-and-divisible-pairs-in-an-array/
Signed-off-by: Matej Focko <me@mfocko.xyz>

go/count-equal-and-divisible-pairs-in-an-array.go

@@ -0,0 +1,34 @@
+package main
+
+import "iter"
+
+type Pair[T, U any] struct {
+	First  T
+	Second U
+}
+type Indices Pair[int, int]
+
+func countPairs(nums []int, k int) int {
+	Pairs := func(n int) iter.Seq[Indices] {
+		return func(yield func(Indices) bool) {
+			for i := 0; i < n; i++ {
+				for j := i + 1; j < n; j++ {
+					if !yield(Indices{i, j}) {
+						return
+					}
+				}
+			}
+		}
+	}
+
+	count := 0
+	for indices := range Pairs(len(nums)) {
+		i, j := indices.First, indices.Second
+
+		if (i*j)%k == 0 && nums[i] == nums[j] {
+			count++
+		}
+	}
+
+	return count
+}