add new solutions

solutions/36/q3640/solution.go

@@ -0,0 +1,59 @@
+package q3640
+
+import "math"
+
+type node struct {
+	pos int
+	dir int8
+}
+
+const (
+	NEUTRAL int8 = iota
+	ASCEND
+	DESCEND
+)
+
+func maxSumTrionic(nums []int) int64 {
+	nodes := [4]node{}
+	pfSum := make([]int, len(nums)+1) // prefix sum
+	pfSum[1] = nums[0]
+	var maxSum = math.MinInt
+
+	var currentDir int8
+	for i := 1; i < len(nums); i++ {
+		switch {
+		case nums[i] == nums[i-1]:
+			currentDir = NEUTRAL
+		case nums[i] < nums[i-1]:
+			currentDir = DESCEND
+		default:
+			currentDir = ASCEND
+		}
+
+		if currentDir != nodes[3].dir {
+			nodes[0], nodes[1], nodes[2] = nodes[1], nodes[2], nodes[3]
+			nodes[3] = node{
+				pos: i,
+				dir: currentDir,
+			}
+			for j := nodes[0].pos + 1; j < nodes[1].pos; j++ {
+				if pfSum[j] < pfSum[nodes[0].pos] {
+					nodes[0].pos = j
+				}
+			}
+		} else {
+			nodes[3].pos = i
+		}
+
+		pfSum[i+1] = nums[i] + pfSum[i]
+
+		if nodes[1].dir == ASCEND && nodes[2].dir == DESCEND && nodes[3].dir == ASCEND {
+			curSum := pfSum[i+1] - pfSum[nodes[0].pos]
+			maxSum = max(curSum, maxSum)
+		}
+	}
+
+	return int64(maxSum)
+}
+
+var _ = maxSumTrionic