Create ReorderList.cpp

Linked Lists/ReorderList.cpp

@@ -0,0 +1,54 @@
+/**
+ * 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) {}
+ * };
+ */
+class Solution {
+public:
+ListNode*reverse(ListNode*head){
+    if(head==NULL){
+        return NULL;
+    }
+    ListNode*prev=NULL;
+    ListNode*forward=NULL;
+    ListNode*curr=head;
+    while(curr!=NULL){
+        forward=curr->next;
+       curr->next=prev;
+        prev=curr;
+        curr=forward;
+    }
+    return prev;
+}
+
+void merge(ListNode*list1,ListNode*list2){
+    while(list2){
+        ListNode*nextNode=list1->next;
+        list1->next=list2;
+        list1=list2;
+        list2=nextNode;
+    }
+}
+    void reorderList(ListNode* head) {
+         if(head==NULL || head->next==NULL){
+        return;
+    }
+    ListNode*fast=head;
+    ListNode*slow=head;
+   ListNode*prev=head;
+    while(fast!=NULL && fast->next!=NULL){
+        prev=slow;
+        fast=fast->next->next;
+        slow=slow->next;
+    }
+   prev->next=NULL;
+   ListNode*list1=head;
+   ListNode*list2=reverse(slow);
+   merge(list1,list2);
+    }
+};