Complete LinkedList-1

Problem49.java

@@ -0,0 +1,17 @@
+// Time Complexity : O(N)
+// Space Complexity : O(1)
+
+class Solution {
+    public ListNode reverseList(ListNode head) {
+        ListNode curr = head;
+        ListNode prev = null;
+
+        while(curr != null) {
+            ListNode temp = curr.next;
+            curr.next = prev;
+            prev = curr;
+            curr = temp;
+        }
+        return prev;
+    }
+}

Problem50.java

@@ -0,0 +1,29 @@
+// Time Complexity : O(N)
+// Space Complexity : O(1)
+
+class Solution {
+    public ListNode removeNthFromEnd(ListNode head, int n) {
+        ListNode dummy = new ListNode (-1);
+        dummy.next = head;
+        int count = 0;
+
+        ListNode slow = dummy;
+        ListNode fast = dummy;
+
+        while (count <= n) {
+            fast = fast.next;
+            count++;
+        }
+
+        while (fast != null){
+            slow = slow.next;
+            fast = fast.next;
+        }
+
+        ListNode temp = slow.next;
+        slow.next = slow.next.next;
+        temp.next = null;
+
+        return dummy.next;
+    }
+}

Problem51.java

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