Merge pull request #2699 from tahzeer/patch-2

Create 2130-maximum-twin-sum-of-a-linked-list.cpp

Author: MHamiid

cpp/2130-maximum-twin-sum-of-a-linked-list.cpp

@@ -0,0 +1,49 @@
+/**
+ * Definition for singly-linked list.
+ * struct ListNode {
+ *     int val;
+ *     ListNode *next;
+ *     ListNode() : val(0), next(nullptr) {}
+ *     ListNode(int x) : val(x), next(nullptr) {}
+ *     ListNode(int x, ListNode *next) : val(x), next(next) {}
+ * };
+ */
+
+// Time: O(n)
+// Space: O(1)
+class Solution {
+public:
+    int pairSum(ListNode* head) {
+        ListNode *fast = head, *slow = head;
+
+        while(fast && fast->next) {
+            slow = slow->next;
+            fast = fast->next->next;
+        }
+        slow = reverseList(slow);
+        
+        int mx = 0;
+        while(head && slow) {
+            mx = max(mx, head->val + slow->val);
+            head = head->next;
+            slow = slow->next;
+        }
+        
+        return mx;
+    }
+private:
+    ListNode* reverseList(ListNode* head) {
+        ListNode* prev = NULL;
+        ListNode* curr = head;
+        ListNode* NEXT = NULL;
+        
+        while(curr) {
+            NEXT = curr->next;
+            curr->next = prev;
+            prev = curr;
+            curr = NEXT;
+        }
+        
+        return prev;
+    }
+};