Hard LeetCode-Java-Solutions S.no Coding Problem 1 Merge K Sorted Lists 2 Serialize and Deserialize a Binary Tree 3 Palindrome Pairs 4 Binary Tree PostOrder Traversal 5 Largest Rectangle in Histogram 6 Trapping Rain Water 7 Parallel Courses 8 LFU Cache 9 Unique Paths III 10 Integer to English Words 11 Number of Valid Subarrays 12 Candy 13 Odd Even Jump 14 Longest Consecutive Sequence 15 Substring with Concatenation of All Words 16 Median of Two Sorted Arrays 17 Hard 18 Longest Substring with At Most K Distinct Characters 19 Closest Binary Search Tree Values II 20 Edit Distance 21 Longest Palindrome Product 22 K Empty Slots 23 Cut Off Trees for Golf Event 24 Word Break II 25 LRU Cache 26 Parsing A Boolean Expression 27 Maximum Frequency Stack 28 N-Queens 29 Sliding Window Maximum 30 Optimal Account Balancing 31 Divide Array Into Increasing Sequences 32 Serialize and Deserialize N-ary Tree 33 Word Search II 34 Insert Delete GetRandom O(1) - Duplicates Allowed 35 Recover a Tree From Preorder Traversal 36 Text Justification 37 Find Median From Data Stream 38 Number of Submatrices That Sum to Target 39 First Missing Positive 40 Minimum Window Substring 41 Stream of Characters 42 Prefix and Suffix Search 43 Longest Substring with At Most Two Distinct Characters 44 Find Minimum in Rotated Sorted Array II 45 Sliding Window Median 46 Basic Calculator 47 Binary Tree Maximum Path Sum 48 Interleaving String 49 Valid Number 50 Robot Room Cleaner 51 Employee Free Time 52 Design Search Autocomplete System 53 Basic Calculator III 54 Longest Increasing Path in a Matrix