Linked-List-1 problems

LinkedListCycle2.java

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+// Time complexity: O(n)
+// Space complexity: O(1)
+
+public class Solution {
+    public ListNode detectCycle(ListNode head) {
+        boolean flag = false;
+        ListNode slow = head;
+        ListNode fast = head;
+
+        while(fast != null && fast.next != null) {
+            slow = slow.next;
+            fast = fast.next.next;
+
+            if(slow == fast) {
+                flag = true;
+                break;
+            }
+        }
+
+        if(!flag) {
+            return null;
+        }
+
+        slow = head;
+        while (fast != slow) {
+            slow = slow.next;
+            fast = fast.next;
+        }
+        return slow;
+    }
+}

RemoveNthNodeFromEnd.java

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+// Time complexity: O(n)
+// Space complexity: O(1)
+class Solution {
+    public ListNode removeNthFromEnd(ListNode head, int n) {
+
+        ListNode dummy = new ListNode(-1, head);
+        ListNode slow = dummy;
+        ListNode fast = dummy;
+
+        for(int i = 0; i <=n; i++) {
+            fast = fast.next;
+        }
+
+        while(fast != null) {
+            slow = slow.next;
+            fast = fast.next;
+        }
+
+        slow.next = slow.next.next;
+        return dummy.next;
+    }
+}

ReverseLinkedList.java

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+/**
+ * 
+ * Time complexity: O(n)
+ * Space complexity: O(1)
+ */
+class Solution {
+    public ListNode reverseList(ListNode head) {
+        ListNode prev = null;
+        ListNode curr = head;
+
+        while(curr != null) {
+            ListNode temp = curr.next;
+            curr.next = prev;
+            prev = curr;
+            curr = temp;
+        }
+        return prev;
+    }
+}