Added algorithm for swapping linkedlist nodes

The above algorithm helps in swapping nodes of linkedlists.

Author: Aashu-11

src/main/java/com/thealgorithms/datastructures/lists/SwapNodes.java

@@ -0,0 +1,96 @@
+// Java program to swap the nodes of a linked list rather
+// than swapping the data from the nodes.
+class Node {
+    int data;
+    Node next;
+
+    Node(int data) {
+        this.data = data;
+        this.next = null;
+    }
+}
+
+public class SwapNodes {
+
+    // Function to swap nodes x and y in linked list by changing links
+    static Node swapNodes(Node head, int x, int y) {
+
+        // Nothing to do if x and y are the same
+        if (x == y) {
+            return head;
+        }
+
+        Node prevX = null, currX = null;
+        Node prevY = null, currY = null;
+        Node curr = head;
+
+        // First loop to find x
+        while (curr != null) {
+            if (curr.data == x) {
+                currX = curr;
+                break;
+            }
+            prevX = curr;
+            curr = curr.next;
+        }
+
+        curr = head;
+
+        // Second loop to find y
+        while (curr != null) {
+            if (curr.data == y) {
+                currY = curr;
+                break;
+            }
+            prevY = curr;
+            curr = curr.next;
+        }
+
+        // If either x or y is not present, nothing to do
+        if (currX == null || currY == null) {
+            return head;
+        }
+
+        // If x is not head of the linked list
+        if (prevX != null) {
+            prevX.next = currY;
+        } else {
+            head = currY;
+        }
+
+        // If y is not head of the linked list
+        if (prevY != null) {
+            prevY.next = currX;
+        } else {
+            head = currX;
+        }
+
+        // Swap next pointers
+        Node temp = currY.next;
+        currY.next = currX.next;
+        currX.next = temp;
+
+        return head;
+    }
+
+    static void printList(Node curr) {
+        while (curr != null) {
+            System.out.print(curr.data + " ");
+            curr = curr.next;
+        }
+        System.out.println();
+    }
+
+    public static void main(String[] args) {
+
+        // Constructed linked list: 1->2->3->4->5
+        Node head = new Node(1);
+        head.next = new Node(2);
+        head.next.next = new Node(3);
+        head.next.next.next = new Node(4);
+        head.next.next.next.next = new Node(5);
+
+        head = swapNodes(head, 4, 3);
+        printList(head);
+    }
+}