add new solutions

solutions/1/q172/solution.go

@@ -0,0 +1,21 @@
+package q172
+
+// Note: actually, counting 5 alone is enough since 2 certainly occurs more than 5.
+
+func trailingZeroes(n int) int {
+	count2, count5 := 0, 0
+	for i := 2; i <= n; i++ {
+		num := i
+		for num%2 == 0 {
+			num /= 2
+			count2++
+		}
+		for num%5 == 0 {
+			num /= 5
+			count5++
+		}
+	}
+	return min(count2, count5)
+}
+
+var _ = trailingZeroes