Solution of Leetcode Problem 234 added

Leetcode Solutions/234_Palindrome_Linked_List.cpp

@@ -0,0 +1,71 @@
+/**
+ * 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* getnode_middle(ListNode* slow,ListNode* fast)
+    {
+        ListNode* temp=nullptr;
+        while(fast!=nullptr&&fast->next!=nullptr)
+        {
+            fast=fast->next->next;
+            temp=slow;
+            slow=slow->next;
+
+        }
+        return temp;
+    }
+
+
+    void inplacereverse(ListNode* last)
+    {
+        ListNode* prev=last->next;
+        ListNode* present=prev->next;
+        ListNode* f;
+        if(present!=nullptr)
+        {
+            f=present->next;
+        }
+        while(present!=nullptr)
+        {
+            present->next=prev;
+            prev=present;
+            present=f;
+            if(f!=nullptr)
+                f=f->next;
+        }
+        last->next->next=nullptr;
+        last->next=prev;
+    }
+
+
+    bool check(ListNode* start,ListNode*secondliststart)
+    {
+        ListNode* breaknode=secondliststart;
+        while(start!=breaknode)
+           { if(start==nullptr||start->val!=secondliststart->val)
+                {return false;}
+            start=start->next;
+            secondliststart=secondliststart->next;}
+        return true;
+    }
+
+    bool isPalindrome(ListNode* head) {
+        if(head==nullptr)
+            return false;
+        if(head->next==nullptr)
+            return true;
+        ListNode* mid=getnode_middle(head,head);
+        inplacereverse(mid);
+        bool ans=check(head,mid->next);
+        inplacereverse(mid);
+        return ans;
+    }
+};