| 502 | IPO | Hard | 2099 | arraygreedysorting+1 |
| 588 | Design In-Memory File System | Hard | 1894 | hash-tablestringdesign+1 |
| 632 | Smallest Range Covering Elements from K Lists | Hard | 2093 | arrayhash-tablegreedy+3 |
| 685 | Redundant Connection II | Hard | 1897 | depth-first-searchbreadth-first-searchunion-find+1 |
| 691 | Stickers to Spell Word | Hard | — | arrayhash-tablestring+5 |
| 699 | Falling Squares | Hard | — | arraysegment-treeordered-set |
| 715 | Range Module | Hard | — | designsegment-treeordered-set |
| 719 | Find K-th Smallest Pair Distance | Hard | 1983 | arraytwo-pointersbinary-search+1 |
| 732 | My Calendar III | Hard | — | binary-searchdesignsegment-tree+2 |
| 745 | Prefix and Suffix Search | Hard | 2002 | hash-tablestringdesign+1 |
| 759 | Employee Free Time | Hard | 1712 | arraysortingheap-priority-queue |
| 765 | Couples Holding Hands | Hard | 1999 | greedydepth-first-searchbreadth-first-search+2 |
| 778 | Swim in Rising Water | Hard | 2097 | arraybinary-searchdepth-first-search+4 |
| 827 | Making A Large Island | Hard | 2151 | arraydepth-first-searchbreadth-first-search+2 |
| 839 | Similar String Groups | Hard | 1861 | arraystringdepth-first-search+2 |
| 843 | Guess the Word | Hard | 1985 | arraymathstring+2 |
| 850 | Rectangle Area II | Hard | 2236 | arraysegment-treeline-sweep+1 |
| 862 | Shortest Subarray with Sum at Least K | Hard | 2307 | arraybinary-searchqueue+4 |
| 879 | Profitable Schemes | Hard | 2204 | arraydynamic-programming |
| 882 | Reachable Nodes In Subdivided Graph | Hard | 2328 | graphheap-priority-queueshortest-path |
| 895 | Maximum Frequency Stack | Hard | 2028 | hash-tablestackdesign+1 |
| 913 | Cat and Mouse | Hard | 2567 | mathdynamic-programminggraph+3 |
| 920 | Number of Music Playlists | Hard | 2400 | mathdynamic-programmingcombinatorics |
| 924 | Minimize Malware Spread | Hard | 1869 | arrayhash-tabledepth-first-search+3 |
| 928 | Minimize Malware Spread II | Hard | 1985 | arrayhash-tabledepth-first-search+3 |
| 952 | Largest Component Size by Common Factor | Hard | 2272 | arrayhash-tablemath+2 |
| 975 | Odd Even Jump | Hard | 2079 | arraydynamic-programmingstack+3 |
| 980 | Unique Paths III | Hard | 1977 | backtrackingbit-manipulationdynamic-programming |
| 992 | Subarrays with K Different Integers | Hard | 2200 | arrayhash-tablesliding-window+2 |
| 1032 | Stream of Characters | Hard | 1891 | arraystringdesign+2 |
| 1074 | Number of Submatrices That Sum to Target | Hard | 2074 | arrayhash-tablematrix+1 |
| 1157 | Online Majority Element In Subarray | Hard | 2205 | arraybinary-searchdesign+2 |
| 1203 | Sort Items by Groups Respecting Dependencies | Hard | 2419 | depth-first-searchbreadth-first-searchgraph+1 |
| 1220 | Count Vowels Permutation | Hard | 1730 | dynamic-programming |
| 1235 | Maximum Profit in Job Scheduling | Hard | 2008 | arraybinary-searchdynamic-programming+1 |
| 1255 | Maximum Score Words Formed by Letters | Hard | 1882 | arrayhash-tablestring+5 |
| 1359 | Count All Valid Pickup and Delivery Options | Hard | 1723 | mathdynamic-programmingcombinatorics |
| 1368 | Minimum Cost to Make at Least One Valid Path in a Grid | Hard | 2069 | arraybreadth-first-searchgraph+3 |
| 1383 | Maximum Performance of a Team | Hard | 2091 | arraygreedysorting+1 |
| 1406 | Stone Game III | Hard | 2027 | arraymathdynamic-programming+1 |
| 1425 | Constrained Subsequence Sum | Hard | 2032 | arraydynamic-programmingqueue+3 |
| 1467 | Probability of a Two Boxes Having The Same Number of Distinct Balls | Hard | 2357 | arraymathdynamic-programming+3 |
| 1489 | Find Critical and Pseudo-Critical Edges in Minimum Spanning Tree | Hard | 2572 | union-findgraphsorting+2 |
| 1499 | Max Value of Equation | Hard | 2456 | arrayqueuesliding-window+2 |
| 1505 | Minimum Possible Integer After at Most K Adjacent Swaps On Digits | Hard | 2337 | stringgreedybinary-indexed-tree+1 |
| 1515 | Best Position for a Service Centre | Hard | 2157 | arraymathgeometry+1 |
| 1547 | Minimum Cost to Cut a Stick | Hard | 2116 | arraydynamic-programmingsorting |
| 1553 | Minimum Number of Days to Eat N Oranges | Hard | 2048 | dynamic-programmingmemoization |
| 1569 | Number of Ways to Reorder Array to Get Same BST | Hard | 2288 | arraymathdivide-and-conquer+7 |
| 1579 | Remove Max Number of Edges to Keep Graph Fully Traversable | Hard | 2132 | union-findgraph |