Adding all the solutions

DetectCycle-2.java

@@ -0,0 +1,44 @@
+// TimeComplexity: O(n)
+// SpaceComplexity: O(1)
+
+public class Solution {
+    public ListNode detectCycle(ListNode head) {
+        ListNode slow = head;
+        ListNode fast = head;
+        boolean flag = false;
+        while(fast != null && fast.next != null) {
+            slow = slow.next;
+            fast = fast.next.next;
+            if(slow == fast) {
+                flag = true;
+                break;
+            }
+
+        }
+        if(flag == false) {
+            return null;
+        }
+        fast = head;
+        while(slow!=fast) {
+            slow = slow.next;
+            fast = fast.next;
+        }
+        return slow;
+    }
+}
+
+// TimeComplexity: O(n)
+// SpaceComplexity: O(n)
+public class Solution {
+    public ListNode detectCycle(ListNode head) {
+        HashSet<ListNode> set = new HashSet<>();
+        while(head!=null) {
+            if(set.contains(head)) {
+                return head;
+            }
+            set.add(head);
+            head = head.next;
+        }
+        return null;
+    }
+}

remove-nth-node-from-end-of-linked-list.java

@@ -0,0 +1,57 @@
+// TimeComplexity: O(n)
+// SpaceComplexity: O(1)
+class Solution {
+    public ListNode removeNthFromEnd(ListNode head, int n) {
+    ListNode dummy = new ListNode(-1, head);
+    ListNode slow = dummy;
+    ListNode fast = dummy;
+    int i =0;
+    while(i<=n) {
+        fast = fast.next;
+        i++;
+    }
+    while(fast != null) {
+        slow = slow.next;
+        fast = fast.next;
+    }
+    ListNode temp = slow.next;
+    slow.next = slow.next.next;
+    temp.next = null;
+    return dummy.next;       
+    }
+}
+
+
+// TimeComplexity: O(2n)
+// SpaceComplexity: O(1)
+
+class Solution {
+    public ListNode removeNthFromEnd(ListNode head, int n) {
+    ListNode first = head;
+    int m=0;
+    while(first!=null) {
+        m++;
+        first = first.next;
+    }
+    System.out.println(m);
+    int k = m-n;
+    if(k==0) {
+        ListNode temp2 =  head;
+        head= head.next;
+        temp2.next = null;
+        return head;
+    }
+    ListNode second = head;
+    for(int i=0; i<k-1; i++){
+        System.out.println(second.val);
+        second= second.next;
+    }
+
+    ListNode temp = second.next;
+    second.next = second.next.next;
+    temp.next = null;
+
+    return head;
+
+    }
+}

reverse-linked-list.java

@@ -0,0 +1,42 @@
+// Solution -1
+
+// TimeComplexity: O(n)
+// SpaceComplexity: O(1)
+
+class Solution {
+    ListNode output;
+    public ListNode reverseList(ListNode head) {
+        helper(head);
+        return output;
+    }
+
+    private void helper(ListNode head) {
+        if(head == null || head.next ==null) {
+            output = head;
+            return;
+        }
+        helper(head.next);
+        head.next.next = head;
+        head.next =null;
+        return;
+    }
+}
+
+// Solution -2 
+
+// TimeComplexity: O(n)
+// SpaceComplexity: O(1)
+
+class Solution {
+    public ListNode reverseList(ListNode head) {
+        ListNode output = null;
+        while(head!=null) {
+            ListNode temp = head;
+            head= head.next;
+            temp.next = output;
+            output = temp;
+        }
+        return output;
+
+    }
+}