two singly list to solve this ploblem

Author: Adam Lin

328_oddEvenList.cpp

@@ -0,0 +1,79 @@
+/**
+ * Definition for singly-linked list.
+ * struct ListNode {
+ *     int val;
+ *     ListNode *next;
+ *     // Constructors
+ *     ListNode() : val(0), next(nullptr) {}
+ *     ListNode(int x) : val(x), next(nullptr) {}
+ *     ListNode(int x, ListNode *next) : val(x), next(next) {}
+ * };
+ */
+class Solution {
+public:
+    ListNode* oddEvenList(ListNode* head) {
+        // If the list is empty or has only one node, return it as is
+        if(head == nullptr) return nullptr;
+
+        // Initialize pointers for odd and even nodes
+        ListNode* odd = head;             // Starts at the first node (odd position)
+        ListNode* even = head->next;      // Starts at the second node (even position)
+        ListNode* evenHead = even;        // Save the head of the even list to attach later
+
+        /* Initial State:
+         *
+         * [1] -> [2] -> [3] -> [4] -> [5] -> NULL
+         *  ^      ^
+         * odd    even
+         *
+         * evenHead points to [2]
+         */
+
+        // Loop until there are no more even nodes
+        while(odd->next != nullptr && even->next != nullptr){
+            // Link current odd node to the next odd node
+            odd->next = even->next;
+            odd = odd->next;              // Move odd pointer to the next odd node
+
+            /* After updating odd pointers:
+             *
+             * [1] -> [3] -> [4] -> [5] -> NULL
+             *         ^
+             *        odd
+             *
+             * [2] -> [3] (still, but will be updated next)
+             * evenHead points to [2]
+             */
+
+            // Link current even node to the next even node
+            even->next = odd->next;
+            even = even->next;            // Move even pointer to the next even node
+
+            /* After updating even pointers:
+             *
+             * [1] -> [3] -> [4] -> [5] -> NULL
+             *         ^
+             *        odd
+             *
+             * [2] -> [4] -> [5] -> NULL
+             *                ^
+             *               even
+             *
+             * evenHead points to [2]
+             */
+        }
+
+        // Attach the even list to the end of the odd list
+        odd->next = evenHead;
+
+        /* Final State:
+         *
+         * [1] -> [3] -> [5] -> [2] -> [4] -> NULL
+         *  ^                       ^
+         * head                    evenHead
+         */
+
+        // Return the head of the rearranged list
+        return head;
+    }
+};