Add solution to day 17

05- May/17- Maximum Twin Sum of a Linked List/17- Maximum Twin Sum of a Linked List (Ahmed Gamal).cpp

@@ -0,0 +1,40 @@
+// Author: Ahmed Gamal
+
+// for this problem, we will use the two pointers technique
+// we want to let one pointer point to the first node after the middle node
+// and the other pointer point to the middle node
+// then we will reverse the first half of the linked list
+// then we will iterate over the two halves and get the maximum sum of the two nodes
+
+// to achieve this, we need to have 4 pointers
+// 1- cur: to iterate over the linked list (will point to the first node after the middle node)
+// 2- fast: the fast pointer to iterate over the linked list and stop the iteration at the middle node
+// 3- nxt: to save the next node of the current node
+// 4- prv: to save the previous node of the current node
+
+// nxt, prv: will be used to reverse the first half of the linked list
+
+class Solution {
+public:
+    int pairSum(ListNode* head) {
+        ListNode *cur, *fast, *nxt, *prv = nullptr;
+        cur = fast = head;
+
+        while(fast) {
+            fast = fast -> next -> next;
+            nxt = cur -> next;
+            cur -> next = prv;
+            prv = cur;
+            cur = nxt;
+        }
+
+        int ans = 0;
+        while(cur) {
+            ans = max(ans, prv -> val + cur -> val);
+            cur = cur -> next;
+            prv = prv -> next;
+        }
+
+        return ans;
+    }
+};