LinkedList 1 completed

Problem1.java

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+// Time Complexity :
+// Space Complexity :
+// Did this code successfully run on Leetcode :
+// Any problem you faced while coding this :
+
+
+// Your code here along with comments explaining your approach
+class Problem1 {
+    public ListNode reverseList(ListNode head) {
+        if(head==null) return head;
+        //return reverseListItr(head);
+        ListNode newHead =  reverseListRecur(head);
+        head.next = null;
+        return newHead;
+
+    }
+    //TC :O(N)
+    //SC :O(1)
+    public ListNode reverseListItr(ListNode head) {
+
+        ListNode prev = null;
+        ListNode curr = head;
+        ListNode temp = null;
+
+        while(curr != null){
+
+            temp=curr.next;
+            curr.next = prev;
+            prev = curr;
+            curr = temp;
+        }
+
+
+        return prev;
+    }
+    //TC :O(N)
+    //SC :O(N)
+    public ListNode reverseListRecur(ListNode node) {
+
+        if(node.next == null){
+            return node;
+        }
+        ListNode nextNode =  reverseListRecur(node.next);
+        node.next.next = node;
+
+        return nextNode;
+    }
+}

Problem2.java

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+// Time Complexity :
+// Space Complexity :
+// Did this code successfully run on Leetcode :
+// Any problem you faced while coding this :
+
+
+// Your code here along with comments explaining your approach
+
+/**
+ * Definition for singly-linked list.
+ * public class ListNode {
+ *     int val;
+ *     ListNode next;
+ *     ListNode() {}
+ *     ListNode(int val) { this.val = val; }
+ *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
+ * }
+ */
+class Problem2 {
+    public ListNode removeNthFromEnd(ListNode head, int n) {
+        ListNode dummy = new ListNode(-1);
+        dummy.next = head;
+        ListNode fast = dummy;
+        ListNode slow = dummy;
+        int count = 0;
+
+        while(count<=n){
+            fast = fast.next;
+            count++;
+        }
+
+        while(fast !=null){
+            fast = fast.next;
+            slow = slow.next;
+        }
+
+        slow.next = slow.next.next;
+
+        return dummy.next;
+    }
+
+}

Problem3.java

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+// Time Complexity :
+// Space Complexity :
+// Did this code successfully run on Leetcode :
+// Any problem you faced while coding this :
+
+
+// Your code here along with comments explaining your approach
+/**
+ * Definition for singly-linked list.
+ * class ListNode {
+ *     int val;
+ *     ListNode next;
+ *     ListNode(int x) {
+ *         val = x;
+ *         next = null;
+ *     }
+ * }
+ */
+public class Probem3 {
+    public ListNode detectCycle(ListNode head) {
+        if(head == null || head.next == null ){
+            return null;
+        }
+        ListNode slow = head;
+        ListNode fast = head;
+
+
+        while (fast != null && fast.next != null) {
+            slow = slow.next;
+            fast = fast.next.next;
+            if (slow == fast) { // Cycle detected
+                break;
+            }
+        }
+
+        if(slow == fast){
+            slow = head;
+
+            while(slow != fast){
+
+                slow = slow.next;
+                fast = fast.next;
+            }
+        }else{
+            return null;
+        }
+
+
+        return fast;
+    }
+}