solves merge 2 linked lists

Author: anishLearnsToCode

README.md

@@ -9,7 +9,7 @@
 | 13 | [Roman To Integer](https://leetcode.com/problems/roman-to-integer/) | Easy | [![Java](https://img.icons8.com/color/40/000000/java-coffee-cup-logo.png)](https://github.com/anishLearnsToCode/leetcode-algorithms/blob/master/src/RomanToInteger.java) |
 | 14 | [Longest Common Prefix](https://leetcode.com/problems/longest-common-prefix/) | Easy | [![Java](https://img.icons8.com/color/40/000000/java-coffee-cup-logo.png)](https://github.com/anishLearnsToCode/leetcode-algorithms/blob/master/src/LongestCommonPrefix.java) |
 | 20 | [ValidParentheses](https://leetcode.com/problems/valid-parentheses/) | Easy | [![Java](https://img.icons8.com/color/40/000000/java-coffee-cup-logo.png)](https://github.com/anishLearnsToCode/leetcode-algorithms/blob/master/src/ValidParentheses.java) |
-| 2 | []() | Easy | |
+| 21 | [Merge 2 Sorted Lists](https://leetcode.com/problems/merge-two-sorted-lists/) | Easy | |
 | 2 | []() | Easy | |
 | 2 | []() | Easy | |
 | 2 | []() | Easy | |

src/Merge2SortedLists.java

@@ -0,0 +1,30 @@
+// https://leetcode.com/problems/merge-two-sorted-lists/
+
+public class Merge2SortedLists {
+    public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
+        ListNode result = new ListNode(-1);
+        ListNode previous = result;
+
+        while (l1 != null && l2 != null) {
+            if (l1.val <= l2.val) {
+                previous.next = l1;
+                l1 = l1.next;
+            } else {
+                previous.next = l2;
+                l2 = l2.next;
+            }
+            previous = previous.next;
+        }
+
+        previous.next = l1 == null ? l2 : l1;
+        return result.next;
+    }
+
+    public static class ListNode {
+        int val;
+        ListNode next;
+        ListNode() {}
+        ListNode(int val) { this.val = val; }
+        ListNode(int val, ListNode next) { this.val = val; this.next = next; }
+    }
+}