Create leetcode 3640

LeetcodeProblems/leetcode 3640

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+class Solution:
+    def maximumSum(self, nums: List[int]) -> int:
+        n = len(nums)
+        NEG = -10**18
+
+        up1 = nums[0]     # first increasing
+        down = NEG        # increasing -> decreasing
+        up2 = NEG         # increasing -> decreasing -> increasing
+
+        ans = NEG
+
+        for i in range(1, n):
+            if nums[i] > nums[i - 1]:
+                new_up2 = max(up2 + nums[i], down + nums[i])
+                new_up1 = max(up1 + nums[i], nums[i])
+                down = down  # unchanged
+            elif nums[i] < nums[i - 1]:
+                new_down = max(down + nums[i], up1 + nums[i])
+                new_up1 = nums[i]
+                new_up2 = NEG
+                down = new_down
+                up1 = new_up1
+                continue
+            else:
+                up1 = nums[i]
+                down = NEG
+                up2 = NEG
+                continue
+
+            up1 = new_up1
+            up2 = new_up2
+            ans = max(ans, up2)
+
+        return ans