| 601 | Human Traffic of Stadium | Hard |
| 629 | K Inverse Pairs Array | Hard |
| 630 | Course Schedule III | Hard |
| 632 | Smallest Range Covering Elements from K Lists | Hard |
| 639 | Decode Ways II | Hard |
| 664 | Strange Printer | Hard |
| 668 | Kth Smallest Number in Multiplication Table | Hard |
| 675 | Cut Off Trees for Golf Event | Hard |
| 679 | 24 Game | Hard |
| 685 | Redundant Connection II | Hard |
| 689 | Maximum Sum of 3 Non-Overlapping Subarrays | Hard |
| 691 | Stickers to Spell Word | Hard |
| 699 | Falling Squares | Hard |
| 710 | Random Pick with Blacklist | Hard |
| 715 | Range Module | Hard |
| 719 | Find K-th Smallest Pair Distance | Hard |
| 726 | Number of Atoms | Hard |
| 730 | Count Different Palindromic Subsequences | Hard |
| 732 | My Calendar III | Hard |
| 736 | Parse Lisp Expression | Hard |
| 741 | Cherry Pickup | Hard |
| 745 | Prefix and Suffix Search | Hard |
| 749 | Contain Virus | Hard |
| 753 | Cracking the Safe | Hard |
| 757 | Set Intersection Size At Least Two | Hard |
| 761 | Special Binary String | Hard |
| 765 | Couples Holding Hands | Hard |
| 768 | Max Chunks To Make Sorted II | Hard |
| 770 | Basic Calculator IV | Hard |
| 773 | Sliding Puzzle | Hard |