Create maximum-alternating-subarray-sum.cpp

Author: kamyu104

C++/maximum-alternating-subarray-sum.cpp

@@ -0,0 +1,19 @@
+// Time:  O(n)
+// Space: O(1)
+
+class Solution {
+public:
+    long long maximumAlternatingSubarraySum(vector<int>& nums) {
+        return max(kadane(nums, 0), kadane(nums, 1));
+    }
+
+private:
+    int64_t kadane(const vector<int>& nums, int start) {
+        int64_t result = numeric_limits<int64_t>::min();
+        for (int64_t i = start, curr = 0, odd = 0; i < size(nums); ++i, odd ^= 1) {
+            curr = !odd ? curr + nums[i] : max(curr - nums[i], 0L);
+            result = max(result, curr);
+        }
+        return result;
+    }
+};