go: add «169. Majority Element»

URL:	https://leetcode.com/problems/majority-element/
Signed-off-by: Matej Focko <me@mfocko.xyz>

go/majority-element.go

@@ -0,0 +1,29 @@
+package main
+
+import (
+	rand "math/rand/v2"
+)
+
+func majorityElement(nums []int) int {
+	DISCARD := -1_000_000_001
+
+	threshold := len(nums) >> 1
+	for {
+		sample := nums[rand.N(len(nums))]
+		if sample == DISCARD {
+			continue
+		}
+
+		counter := 0
+		for i, x := range nums {
+			if x == sample {
+				counter++
+				nums[i] = DISCARD
+			}
+
+			if counter > threshold {
+				return sample
+			}
+		}
+	}
+}