LC#206 reverse a given linkedlist, iterative & recursive approach

Author: NirmalSilwal

Leetcode/leetcodeTags/LinkedList/ReverseLinkedList206.java

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+package LinkedList;
+
+public class ReverseLinkedList206 {
+
+	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;
+		}
+	}
+
+	// using recursion
+	public ListNode reverseList(ListNode head) {
+		return recursiveReverse(head);
+	}
+
+	private ListNode recursiveReverse(ListNode head) {
+
+		if (head == null || head.next == null)
+			return head;
+
+		ListNode newHead = recursiveReverse(head.next);
+
+		head.next.next = head;
+		head.next = null;
+
+		return newHead;
+	}
+
+	// using iterative approach
+	public ListNode reverseListIterative(ListNode head) {
+
+		if (head == null || head.next == null)
+			return head;
+
+		ListNode prev = head;
+		ListNode curr = head.next;
+		ListNode nextNode = head.next.next;
+		prev.next = null; // head node pointing to null as it will be tail at the end
+
+		while (curr.next != null) {
+			curr.next = prev;
+			prev = curr;
+			curr = nextNode;
+			nextNode = curr.next;
+		}
+
+		// pointing last node to second last node
+		curr.next = prev;
+
+		return curr;
+	}
+
+}