go: add «135. Candy»

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

go/candy.go

@@ -0,0 +1,37 @@
+package main
+
+func candy(ratings []int) int {
+	n := len(ratings)
+
+	given, i := n, 1
+	for i < n {
+		if ratings[i-1] == ratings[i] {
+			// same rating ⇒ no need for adjustments
+			i++
+			continue
+		}
+
+		// increasing rating
+		localMax := 0
+		for ; i < n && ratings[i-1] < ratings[i]; i++ {
+			localMax += 1
+			given += localMax
+		}
+
+		if i >= n {
+			return given
+		}
+
+		// decreasing rating
+		localMin := 0
+		for ; i < n && ratings[i-1] > ratings[i]; i++ {
+			localMin += 1
+			given += localMin
+		}
+
+		// count the extrema only once
+		given -= min(localMin, localMax)
+	}
+
+	return given
+}