go: add «719. Find K-th Smallest Pair Distance»

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

go/find-k-th-smallest-pair-distance.go

@@ -0,0 +1,37 @@
+package main
+
+import "slices"
+
+func smallestDistancePair(nums []int, k int) int {
+	pairsWithMaxDistance := func(distance int) int {
+		count := 0
+
+		left := 0
+		for right := 0; right < len(nums); right++ {
+			for nums[right]-nums[left] > distance {
+				left++
+			}
+
+			count += right - left
+		}
+
+		return count
+	}
+
+	slices.Sort(nums)
+
+	low, high := 0, nums[len(nums)-1]-nums[0]
+
+	for low < high {
+		mid := (low + high) / 2
+		count := pairsWithMaxDistance(mid)
+
+		if count < k {
+			low = mid + 1
+		} else {
+			high = mid
+		}
+	}
+
+	return low
+}