merge two sorted list

Author: Antesh Sharma

src/main/java/com/antesh/dsa/linkedlist/MergeTwoSortedList.java

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+package com.antesh.dsa.linkedlist;
+
+/**
+ * Problem Reference: https://github.com/aniketskulkarni/coding-problems/blob/master/LeetCode/src/com/java7/problem/easy/linkedlist/MergeTwoSortedLists.java
+ * You are given the heads of two sorted linked lists list1 and list2.
+ * Merge the two lists in a one sorted list. The list should be made by splicing
+ * together the nodes of the first two lists.
+ * Return the head of the merged linked list. Duplicate nodes should be retained.
+ *
+ * Input: list1 = [1,2,4], list2 = [1,3,4]
+ * Output: [1,1,2,3,4,4]
+ *
+ * Input: list1 = [], list2 = []
+ * Output: []
+ */
+public class MergeTwoSortedList {
+
+    class Node {
+        int data;
+        Node next;
+
+        public Node(int data) {
+            this.data = data;
+        }
+    }
+
+    public Node addToTail(Node head, int data) {
+        if (head == null) {
+            return new Node(data);
+        }
+        Node temp = new Node(data);
+        Node ptr = head;
+        while (ptr.next != null) {
+            ptr = ptr.next;
+        }
+
+        ptr.next = temp;
+        return head;
+    }
+
+    public String print(Node node) {
+        StringBuilder sb = new StringBuilder();
+        Node ptr = node;
+        while (ptr != null) {
+            sb.append(ptr.data).append(" --> ");
+            ptr = ptr.next;
+        }
+
+        return sb.toString();
+    }
+
+    public Node mergeTwoSortedList(Node n1,Node n2) {
+        if (n1 == null && n2 == null) {
+            return null;
+        }
+
+        if (n1 == null) {
+            return n2;
+        }
+
+        if (n2 == null) {
+            return n1;
+        }
+
+        Node mergeList = null;
+        while (n1 != null && n2 != null) {
+            if (n1.data < n2.data) {
+                mergeList = addToTail(mergeList, n1.data);
+                n1 = n1.next;
+            } else {
+                mergeList = addToTail(mergeList, n2.data);
+                n2 = n2.next;
+            }
+        }
+
+        while (n1 != null) {
+            mergeList = addToTail(mergeList, n1.data);
+            n1 = n1.next;
+        }
+
+        while (n2 != null) {
+            mergeList = addToTail(mergeList, n2.data);
+            n2 = n2.next;
+        }
+
+        return mergeList;
+    }
+
+    public static void main(String[] args) {
+        MergeTwoSortedList list = new MergeTwoSortedList();
+
+        Node sortedList1 = null;
+        for (int i = 1; i < 4; i++) {
+            sortedList1 = list.addToTail(sortedList1, i);
+        }
+
+        Node sortedList2 = null;
+        for (int i = 2; i < 5; i++) {
+            sortedList2 = list.addToTail(sortedList2, i);
+        }
+
+        System.out.println("sortedList1 : " + list.print(sortedList1));
+        System.out.println("sortedList2 : " + list.print(sortedList2));
+        System.out.println("merged list : " + list.print(list.mergeTwoSortedList(sortedList1, sortedList2)));
+
+    }
+}