Linked List [Reorder]

RokibulHasan7 · web-flow · commit 873bf46bda7c · 2022-02-22T22:26:31.000+06:00
diff --git a/Solutions/143.cpp b/Solutions/143.cpp
@@ -0,0 +1,61 @@
+/**
+ * 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* rev(ListNode* head){
+        if(head == NULL){
+            return NULL;
+        }
+        
+        ListNode* prev = NULL;
+        ListNode* curr = head;
+        ListNode* next;
+        while(curr){
+            next = curr -> next;
+            curr -> next = prev;
+            prev = curr;
+            curr = next;     
+        }
+        
+        return prev;
+    }
+    void reorderList(ListNode* head) {
+        if(head==NULL||head->next==NULL||head->next->next==NULL){
+            return;
+        }
+        /// Find middle Node
+        ListNode* slow = head;
+        ListNode* fast = head -> next;
+        
+        while(fast && fast -> next){
+            slow = slow -> next;
+            fast = fast -> next -> next;
+        }
+        
+        ListNode* secHead = slow -> next;
+        slow -> next = NULL;
+        
+        /// Reverse 2nd list
+        secHead = rev(secHead);
+        ListNode* tmp1 = head;
+        ListNode* tmp2 = secHead;
+        
+        while(tmp1 && tmp2){
+            ListNode* curr1 = tmp1 -> next;
+            ListNode* curr2 = tmp2 -> next;
+            
+            tmp1 -> next = tmp2;
+            tmp2 -> next = curr1;
+            tmp1 = curr1;
+            tmp2 = curr2;
+        }
+    }
+};
