Create 1721_SwappingNodes_in_LinkedList.cpp

Author: code1511

Linked_List/1721_SwappingNodes_in_LinkedList.cpp

@@ -0,0 +1,41 @@
+//Method one
+/**
+ * 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* swapNodes(ListNode* head, int k) {
+        ListNode*p=head;
+        ListNode*q=head;
+        int a=k-1;
+        int l=0;
+        while(p){
+            l++,p=p->next;
+        }
+        int b=(l-k);
+
+        p=head;
+        while(a){
+            p=p->next;
+            a--;
+        }
+        while(b){
+            q=q->next;
+            b--;
+        }
+        swap(p->val,q->val);
+        return head;
+    }
+};
+
+
+//method two another approach
+// slow fast pointer
+// k from end = ans 2k+1 from start