reverse a linkedList in TC o(n) and SC: O(1)

Author: Antesh Sharma

src/main/java/com/antesh/dsa/ReverseALinkedList.java

@@ -0,0 +1,93 @@
+package com.antesh.dsa;
+
+/*  Given a linked list, output it's reverse
+
+    - Initialize three pointers prev as NULL, curr as head and next as NULL.
+    - Iterate through the linked list. In loop, do following.
+        // Before changing next of current,
+        // store next node
+        next = curr->next
+        // Now change next of current
+        // This is where actual reversing happens
+        curr->next = prev
+        // Move prev and curr one step forward
+        prev = curr
+        curr = next
+
+    Time Complexity: O(n)
+    Space Complexity: O(1)
+
+*/
+public class ReverseALinkedList {
+
+    static Node root;
+
+    static class Node {
+        int data;
+        Node next;
+
+        public Node(int data) {
+            this.data = data;
+            this.next = null;
+        }
+    }
+
+    public static Node insert(Node root, int data) {
+        if (root == null) {
+            return new Node(data);
+        }
+
+        Node temp = new Node(data);
+        Node ptr = root;
+        while (ptr.next != null) {
+            ptr = ptr.next;
+        }
+        ptr.next = temp;
+
+        return root;
+    }
+
+    public static Node reverse(Node head) {
+        if (head == null) {
+            return head;
+        }
+
+        Node prev = null;
+        Node curr = head;
+        Node temp = null;
+
+        while (curr != null) {
+            temp = curr.next;
+            curr.next = prev;
+            prev = curr;
+            curr = temp;
+        }
+
+        head = prev;
+        return head;
+    }
+
+    public static void print(Node root) {
+        while (root != null) {
+            System.out.print(root.data + " ");
+            root = root.next;
+        }
+    }
+
+    public static void main(String[] args) {
+        int[] arr = {10, 20, 30, 40, 50};
+        for (int i = 0; i < arr.length; i++) {
+            root = insert(root, arr[i]);
+        }
+
+        System.out.println("Print input list: ");
+        print(root);
+
+        System.out.println();
+        root = reverse(root);
+        System.out.println("Print reversed list: ");
+        print(root);
+
+
+    }
+}