add: leetcode 396 solution

leetcode/0396.Rotate-Function/396. Rotate Function.go

@@ -0,0 +1,18 @@
+package leetcode
+
+func maxRotateFunction(nums []int) int {
+	n := len(nums)
+	var sum, f int
+	for i, num := range nums {
+		sum += num
+		f += i * num // F(0)
+	}
+	ans := f
+	for i := 1; i < n; i++ {
+		f += sum - n*nums[n-i] // F(i) = F(i-1) + sum - n*nums[n-i]
+		if f > ans {
+			ans = f
+		}
+	}
+	return ans
+}