Completed Linked-List-1 Assignment

LL_cycle_II.java

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+// Time Complexity : O(n)
+// Space Complexity : O(1)
+// Did this code successfully run on Leetcode : yes
+public class LL_cycle_II {
+    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;
+            } 
+        }
+        fast = head; 
+        if(!flag) return null;
+        while(slow!=fast){
+            slow=slow.next;
+            fast=fast.next;
+        }
+        return slow;
+    }
+}

remove_nth_node.java

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+// Time Complexity : O(n)
+// Space Complexity : O(1)
+// Did this code successfully run on Leetcode :yes 
+class Solution {
+    public ListNode removeNthFromEnd(ListNode head, int n) {
+        ListNode dummy = new ListNode(-1);
+        dummy.next = head;
+        ListNode slow= dummy;
+        ListNode fast = dummy;
+        int cnt=0;
+        while(cnt<=n){
+            fast = fast.next;
+            cnt++;
+        }
+        while(fast!=null){
+            slow=slow.next;
+            fast=fast.next;
+        }
+        ListNode temp = slow.next;
+        slow.next = slow.next.next;
+        temp.next = null;
+        return dummy.next; // head is no longer the orginal head if it was deleted
+
+    }
+}

reverse_ll.java

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+// Time Complexity : O(n)
+// Space Complexity :O(1)
+// Did this code successfully run on Leetcode : yes 
+// we use 3 pointers to reverse the list by storing the values with which we loose connection 
+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;
+            // System.out.println(curr);
+        }
+        return prev;
+    }
+}