Leetcode problems - JAVA solution

The problems are distributed into three packages based on their difficulty level, namely; easy, medium and hard. I have tried to keep the file names as close to the title as possible.

EASY

Title	Solution
1. Two Sum	java
7. Reverse Integer	java
13. Roman to Integer	java
14. Longest Common Prefix	java
20. Valid Parentheses	java
21. Merge Two Sorted Lists	java
28. Implement strStr()	java
53. Maximum Subarray	java
58. Length of Last Word	java
66. Plus One	java
67. Add Binary	java
70. Climbing Stairs	java
83. Remove Duplicates from Sorted List	java
88. Merge Sorted Array	java
100. Same Tree	java
101. Symmetric Tree	java
104. Maximum Depth of Binary Tree	java
107. Binary Tree Level Order Traversal II	java
108. Convert Sorted Array to Binary Search Tree	java
110. Balanced Binary Tree	java
111. Minimum Depth of Binary Tree	java
112. Path Sum	java
121. Best Time to Buy and Sell Stock	java
122. Best Time to Buy and Sell Stock II	java
125. Valid Palindrome	java
136. Single Number	java
141. Linked List Cycle	java
155. Min Stack	java
160. Intersection of Two Linked Lists	java
167. Two Sum II - Input array is sorted	java
169. Majority Element	java
198. House Robber	java
202. Happy Number	java
203. Remove Linked List Elements	java
206. Reverse Linked List	java
217. Contains Duplicate	java
219. Contains Duplicate II	java
226. Invert Binary Tree	java
231. Power of Two	java
232. Implement Queue using Stacks	java
234. Palindrome Linked List	java
235. Lowest Common Ancestor of a Binary Search Tree	java
237. Delete Node in a Linked List	java
242. Valid Anagram	java
252. Meeting Rooms	java
257. Binary Tree Paths	java
258. Add Digits	java
268. Missing Number	java
270. Closest Binary Search Tree Value	java
283. Move Zeroes	java
303. Range Sum Query - Immutable	java
344. Reverse String	java
345. Reverse Vowels of a String	java
346. Moving Average from Data Stream	java
374. Guess Number Higher or Lower	java
387. First Unique Character in a String	java
404. Sum of Left Leaves	java
412. Fizz Buzz	java
426. Convert Binary Search Tree to Sorted Doubly Linked List	java
429. N-ary Tree Level Order Traversal	java
434. Number of Segments in a String	java
437. Path Sum III	java
438. Find All Anagrams in a String	java
441. Arranging Coins	java
442. Find All Duplicates in an Array	java
445. Add Two Numbers II	java
448. Find All Numbers Disappeared in an Array	java
449. Serialize and Deserialize BST	java
450. Delete Node in a BST	java
451. Sort Characters By Frequency	java
452. Minimum Number of Arrows to Burst Balloons	java
459. Repeated Substring Pattern	java
482. License Key Formatting	java
501. Find Mode in Binary Search Tree	java
508. Most Frequent Subtree Sum	java
509. Fibonacci Number	java
510. Inorder Successor in BST II	java
513. Find Bottom Left Tree Value	java
520. Detect Capital	java
530. Minimum Absolute Difference in BST	java
536. Construct Binary Tree from String	java
538. Convert BST to Greater Tree	java
543. Diameter of Binary Tree	java
551. Student Attendance Record I	java
559. Maximum Depth of N-ary Tree	java
560. Subarray Sum Equals K	java
567. Permutation in String	java
572. Subtree of Another Tree	java
588. Design In-Memory File System	java
589. N-ary Tree Preorder Traversal	java
590. N-ary Tree Postorder Traversal	java
605. Can Place Flowers	java
606. Construct String from Binary Tree	java
617. Merge Two Binary Trees	java
637. Average of Levels in Binary Tree	java
645. Set Mismatch	java
653. Two Sum IV - Input is a BST	java
657. Robot Return to Origin	java
658. Find K Closest Elements	java
669. Trim a Binary Search Tree	java
671. Second Minimum Node In a Binary Tree	java
675. Cut Off Trees for Golf Event	java
676. Implement Magic Dictionary	java
680. Valid Palindrome II	java
690. Employee Importance	java
692. Top K Frequent Words	java
694. Number of Distinct Islands	java
700. Search in a Binary Search Tree	java
701. Insert into a Binary Search Tree	java
705. Design HashSet	java
709. To Lower Case	java
719. Find K-th Smallest Pair Distance	java
733. Flood Fill	java
735. Asteroid Collision	java
746. Min Cost Climbing Stairs	java
759. Employee Free Time	java
776. Split BST	java
783. Minimum Distance Between BST Nodes	java
811. Subdomain Visit Count	java
814. Binary Tree Pruning	java
819. Most Common Word	java
863. All Nodes Distance K in Binary Tree	java
872. Leaf-Similar Trees	java
876. Middle of the Linked List	java
896. Monotonic Array	java
897. Increasing Order Search Tree	java
904. Fruit Into Baskets	java
929. Unique Email Addresses	java
937. Reorder Data in Log Files	java
938. Range Sum of BST	java
957. Prison Cells After N Days	java
958. Check Completeness of a Binary Tree	java
965. Univalued Binary Tree	java
973. K Closest Points to Origin	java
980. Unique Paths III	java
986. Interval List Intersections	java
987. Vertical Order Traversal of a Binary Tree	java
988. Smallest String Starting From Leaf	java
1015. Smallest Integer Divisible by K	java
1020. Number of Enclaves	java
1022. Sum of Root To Leaf Binary Numbers	java
1026. Maximum Difference Between Node and Ancestor	java
1028. Recover a Tree From Preorder Traversal	java
1037. Valid Boomerang	java
1038. Binary Search Tree to Greater Sum Tree	java
1047. Remove All Adjacent Duplicates In String	java
1064. Fixed Point	java
1085. Sum of Digits in the Minimum Number	java
1086. High Five	java
1099. Two Sum Less Than K	java
1100. Find K-Length Substrings With No Repeated Characters	java
1108. Defanging an IP Address	java
1119. Remove Vowels from a String	java
1123. Lowest Common Ancestor of Deepest Leaves	java
1134. Armstrong Number	java
1137. N-th Tribonacci Number	java
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