Up to date (2015-02-24), there are total 189 problems on LeetCode Online Judge.
The number of problems is increasing recently.
Here is the classification of all 189 problems.
I'll keep updating for full summary and better solutions. Stay tuned for updates.
- Bit Manipulation
- Array
- String
- Linked List
- Stack
- Heap
- Tree
- Hash Table
- Data Structure
- Math
- Two Pointer
- Sort
- Brute Force Search
- Divide and Conquer
- Binary Search
- Breadth-First Search
- Depth-First Search
- Dynamic Programming
- Backtracking
- Greedy
##Bit Manipulation
| Problem | Solution | Time | Space | Difficulty | Notes |
|---|---|---|---|---|---|
| Single Number | single-number.py | O(n) | O(1) | Medium | |
| Single Number II | single-number-ii.py | O(n) | O(1) | Medium |
##Array
##String
| Problem | Solution | Time | Space | Difficulty | Notes |
|---|---|---|---|---|---|
| Add Binary | add-binary.py | O(n) | O(1) | Easy | |
| Compare Version Numbers | compare-version-numbers.py | O(n) | O(1) | Easy | |
| Count and Say | count-and-say.py | O(n * 2^n) | O(2^n) | Easy | |
| Implement strStr() | implement-strstr.py | O(n + m) | O(m) | Easy | KMP Algorithm |
| Length of Last Word | length-of-last-word.py | O(n) | O(1) | Easy | |
| Longest Common Prefix | longest-common-prefix.py | O(n1 + n2 + ...) | O(1) | Easy | |
| Longest Palindromic Substring | longest-palindromic-substring.py | O(n) | O(n) | Medium | Manacher's Algorithm |
| Multiply Strings | multiply-strings.py | O(m * n) | O(m + n) | Medium | |
| One Edit Distance | one-edit-distance.py | O(m + n) | O(1) | Medium | |
| Reverse Words in a String | reverse-words-in-a-string.py | O(n) | O(n) | Medium | |
| Reverse Words in a String II | reverse-words-in-a-string-ii.py | O(n) | O(1) | Medium | |
| String to Integer (atoi) | string-to-integer-atoi.py | O(n) | O(1) | Easy | |
| Text Justification | text-justification.py | O(n) | O(1) | Hard | |
| Valid Palindrome | valid-palindrome.py | O(n) | O(1) | Easy | |
| ZigZag Conversion | zigzag-conversion.py | O(n) | O(1) | Easy |
##Linked List
| Problem | Solution | Time | Space | Difficulty | Notes |
|---|---|---|---|---|---|
| Add Two Numbers | add-two-numbers.py | O(n) | O(1) | Medium | |
| Copy List with Random Pointer | copy-list-with-random-pointer.py | O(n) | O(1) | Hard | |
| Intersection of Two Linked Lists | intersection-of-two-linked-lists.py | O(m + n) | O(1) | Easy | |
| Remove Duplicates from Sorted List | remove-duplicates-from-sorted-list.py | O(n) | O(1) | Easy | |
| Remove Duplicates from Sorted List II | remove-duplicates-from-sorted-list-ii.py | O(n) | O(1) | Medium | |
| Reverse Linked List II | reverse-linked-list-ii.py | O(n) | O(1) | Medium | |
| Reverse Nodes in k-Group | reverse-nodes-in-k-group.py | O(n) | O(1) | Hard | |
| Rotate List | rotate-list.py | O(n) | O(1) | Medium | |
| Swap Nodes in Pairs | swap-nodes-in-pairs.py | O(n) | O(1) | Medium |
##Stack
| Problem | Solution | Time | Space | Difficulty | Notes |
|---|---|---|---|---|---|
| Binary Search Tree Iterator | binary-search-tree-iterator.py | O(1) | O(h) | Medium | |
| Evaluate Reverse Polish Notation | evaluate-reverse-polish-notation.py | O(n) | O(n) | Medium | |
| Longest Valid Parentheses | longest-valid-parentheses.py | O(n) | O(1) | Hard | |
| Min Stack | min-stack.py | O(n) | O(1) | Easy | |
| Simplify Path | simplify-path.py | O(n) | O(n) | Medium | |
| Symmetric Tree | symmetric-tree.py | O(n) | O(h) | Easy | |
| Valid Parentheses | valid-parentheses.py | O(n) | O(n) | Easy |
##Heap
| Problem | Solution | Time | Space | Difficulty | Notes |
|---|---|---|---|---|---|
| Merge k Sorted Lists | merge-k-sorted-lists.py | O(nlogk) | O(1) | Hard |
##Tree
| Problem | Solution | Time | Space | Difficulty | Notes |
|---|---|---|---|---|---|
| Binary Tree Preorder Traversal | binary-tree-preorder-traversal.py | O(n) | O(1) | Medium | Morris Traversal |
| Binary Tree Inorder Traversal | binary-tree-inorder-traversal.py | O(n) | O(1) | Medium | Morris Traversal |
| Binary Tree Postorder Traversal | binary-tree-postorder-traversal.py | O(n) | O(1) | Hard | Morris Traversal |
| Recover Binary Search Tree | recover-binary-search-tree.py | O(n) | O(1) | Hard | Morris Traversal |
##Hash Table
| Problem | Solution | Time | Space | Difficulty | Notes |
|---|---|---|---|---|---|
| 4 Sum | 4sum.py | O(n^2) ~ O(n^4) | O(n^2) | Medium | |
| Anagrams | anagrams.py | O(n) | O(n) | Medium | |
| Longest Substring with At Most Two Distinct Characters | longest-substring-with-at-most-two-distinct-characters.py | O(n^2) | O(1) | Hard | |
| Longest Substring Without Repeating Characters | longest-substring-without-repeating-characters.py | O(n) | O(1) | Medium | |
| Max Points on a Line | max-points-on-a-line.py | O(n^2) | O(n) | Hard | |
| Minimum Window Substring | minimum-window-substring.py | O(n) | O(k) | Hard | |
| Repeated DNA Sequences | repeated-dna-sequences.py | O(n) | O(n) | Medium | |
| Substring with Concatenation of All Words | substring-with-concatenation-of-all-words.py | O(m * n * k) | O(n * k) | Hard | |
| Two Sum | two-sum.py | O(n) | O(n) | Medium | |
| Two Sum III - Data structure design | two-sum-iii-data-structure-design.py | O(n) | O(n) | Easy | |
| Valid Sudoku | valid-sudoku.py | O(n^2) | O(n) | Easy |
##Data Structure
| Problem | Solution | Time | Space | Difficulty | Notes |
|---|---|---|---|---|---|
| LRU Cache | lru-cache.py | O(1) | O(n) | Hard |
##Math
| Problem | Solution | Time | Space | Difficulty | Notes |
|---|---|---|---|---|---|
| Divide Two Integers | divide-two-integers.py | O(logn) | O(1) | Medium | |
| Excel Sheet Column Title | excel-sheet-column-title.py | O(logn) | O(1) | Easy | |
| Excel Sheet Column Number | excel-sheet-column-number.py | O(n) | O(1) | Easy | |
| Factorial Trailing Zeroes | factorial-trailing-zeroes.py | O(logn) | O(1) | Easy | |
| Fraction to Recurring Decimal | fraction-to-recurring-decimal.py | O(logn) | O(1) | Medium | |
| Gray Code | gray-code.py | O(2^n) | O(1) | Medium | |
| Integer to Roman | integer-to-roman.py | O(n) | O(1) | Medium | |
| Palindrome Number | palindrome-number.py | O(1) | O(1) | Easy | |
| Permutation Sequence | permutation-sequence.py | O(n) | O(1) | Medium | Cantor Ordering |
| Reverse Integer | reverse-integer.py | O(logn) | O(1) | Easy | |
| Roman to Integer | roman-to-integer.py | O(n) | O(1) | Easy | |
| Valid Number | valid-number.py | O(n) | O(1) | Hard | Automata |
##Sort
| Problem | Solution | Time | Space | Difficulty | Notes |
|---|---|---|---|---|---|
| Insert Interval | insert-interval.py | O(n) | O(1) | Hard | |
| Insertion Sort List | insertion-sort-list.py | O(n^2) | O(1) | Medium | |
| Largest Number | largest-number.py | O(n^2) | O(n) | Medium | |
| Maximum Gap | maximum-gap.py | O(n) | O(n) | Hard | Tricky |
| Merge Intervals | merge-intervals.py | O(nlogn) | O(1) | Hard | |
| Merge Sorted Array | merge-sorted-array.py | O(n) | O(1) | Easy | |
| Merge Two Sorted Lists | merge-two-sorted-lists.py | O(n) | O(1) | Easy | |
| Sort Colors | sort-colors.py | O(n) | O(1) | Medium | |
| Sort List | sort-list.py | O(nlogn) | O(logn) | Medium |
##Two Pointer
| Problem | Solution | Time | Space | Difficulty | Notes |
|---|---|---|---|---|---|
| Linked List Cycle | linked-list-cycle.py | O(n) | O(1) | Medium | |
| Linked List Cycle II | linked-list-cycle-ii.py | O(n) | O(1) | Medium | |
| Partition List | partition-list.py | O(n) | O(1) | Medium | |
| Remove Nth Node From End of List | remove-nth-node-from-end-of-list.py | O(n) | O(1) | Easy | |
| Reorder List | reorder-list.py | O(n) | O(1) | Medium | |
| Two Sum II - Input array is sorted | two-sum-ii-input-array-is-sorted.py | O(n) | O(1) | Medium |
##Brute Force Search
| Problem | Solution | Time | Space | Difficulty | Notes |
|---|---|---|---|---|---|
| Letter Combinations of a Phone Number | letter-combinations-of-a-phone-number.py | O(n * 4^n) | O(n) | Medium | |
| Permutations | permutations.py | O(n!) | O(n) | Medium | |
| Permutations II | permutations-ii.py | O(n!) | O(n) | Hard | |
| Subsets | subsets.py | O(n * 2^n) | O(1) | Medium | |
| Subsets II | subsets-ii.py | O(n * 2^n) | O(1) | Medium |
##Divide and Conquer
##Binary Search
| Problem | Solution | Time | Space | Difficulty | Notes |
|---|---|---|---|---|---|
| Find Minimum in Rotated Sorted Array | find-minimum-in-rotated-sorted-array.py | O(logn) | O(1) | Medium | |
| Find Minimum in Rotated Sorted Array II | find-minimum-in-rotated-sorted-array-ii.py | O(logn) ~ O(n) | O(1) | Hard | |
| Find Peak Element | find-peak-element.py | O(logn) | O(1) | Medium | |
| Median of Two Sorted Arrays | median-of-two-sorted-arrays.py | O(log(m + n) | O(1) | Hard | |
| Pow(x, n) | powx-n.py | O(logn) | O(logn) | Medium | |
| Search a 2D Matrix | search-a-2d-matrix.py | O(log m + logn) | O(1) | Medium | |
| Search for a Range | search-for-a-range.py | O(logn) | O(1) | Medium | |
| Search in Rotated Sorted Array | search-in-rotated-sorted-array.py | O(logn) | O(1) | Hard | |
| Search in Rotated Sorted Array II | search-in-rotated-sorted-array-ii.py | O(logn) | O(1) | Medium | |
| Search Insert Position | search-insert-position.py | O(logn) | O(1) | Medium | |
| Sqrt(x) | sqrtx.py | O(logn) | O(1) | Medium |
##Breadth-First Search
| Problem | Solution | Time | Space | Difficulty | Notes |
|---|---|---|---|---|---|
| Binary Tree Level Order Traversal | binary-tree-level-order-traversal.py | O(n) | O(n) | Easy | |
| Binary Tree Level Order Traversal II | binary-tree-level-order-traversal-ii.py | O(n) | O(n) | Easy | |
| Binary Tree Zigzag Level Order Traversal | binary-tree-zigzag-level-order-traversal.py | O(n) | O(n) | Medium | |
| Clone Graph | clone-graph.py | O(n) | O(n) | Medium | |
| Populating Next Right Pointers in Each Node II | populating-next-right-pointers-in-each-node-ii.py | O(n) | O(1) | Hard | |
| Surrounded Regions | surrounded-regions.py | O(m * n) | O(m + n) | Medium | |
| Word Ladder | word-ladder.py | O(n * d) | O(d) | Medium |
##Depth-First Search
| Problem | Solution | Time | Space | Difficulty | Notes |
|---|---|---|---|---|---|
| Combination Sum | combination-sum.py | O(n^m) | O(m) | Medium | |
| Combination Sum II | combination-sum-ii.py | O(n! / m!(n-m)!) | O(m) | Medium | |
| Combinations | combinations.py | O(n!) | O(n) | Medium | |
| Generate Parentheses | generate-parentheses.py | O(4^n / n^(3/2)) | O(n) | Medium | |
| N-Queens | n-queens.py | O(n!) | O(n) | Hard | |
| N-Queens-II | n-queens-ii.py | O(n!) | O(n) | Hard | |
| Palindrome Partitioning | palindrome-partitioning.py | O(n^2) ~ O(2^n) | O(n^2) | Medium | |
| Path Sum | path-sum.py | O(n) | O(h) | Easy | |
| Path Sum II | path-sum-ii.py | O(n) | O(h) | Medium | |
| Restore IP Addresses | restore-ip-addresses.py | O(n^m) ~ O(3^4) | O(n * m) ~ O(3 * 4) | Medium | |
| Sudoku Solver | sudoku-solver.py | O((9!)^9) | O(1) | Hard | |
| Word Search | word-search.py | O(m * n * 3^p) | O(m * n * p) | Medium |
##Dynamic Programming
##Backtracking
| Problem | Solution | Time | Space | Difficulty | Notes |
|---|---|---|---|---|---|
| Word Ladder II | word-ladder-ii.py | O(n * d) | O(d) | Hard |
##Greedy
| Problem | Solution | Time | Space | Difficulty | Notes |
|---|---|---|---|---|---|
| Best Time to Buy and Sell Stock II | best-time-to-buy-and-sell-stock-ii.py | O(n) | O(1) | Medium | |
| Candy | candy.py | O(n) | O(n) | Hard | |
| Container With Most Water | container-with-most-water.py | O(n) | O(1) | Medium | |
| Gas Station | gas-station.py | O(n) | O(1) | Medium | |
| Jump Game | jump-game.py | O(n) | O(1) | Medium | |
| Jump Game II | jump-game-ii.py | O(n^2) | O(1) | Hard | |
| Largest Rectangle in Histogram | largest-rectangle-in-histogram.py | O(n) | O(n) | Hard | Tricky |
| Trapping Rain Water | trapping-rain-water.py | O(n) | O(1) | Hard | Tricky |
| Wildcard Matching | wildcard-matching.py | O(m + n) | O(1) | Hard | Tricky |
##SQL
| Problem | Solution | Time | Space | Difficulty | Notes |
|---|---|---|---|---|---|
| Combine Two Tables | combine-two-tables.sql | O(m + n) | O(m + n) | Easy | |
| Consecutive Numbers | consecutive-numbers.sql | O(n) | O(n) | Medium | |
| Customers Who Never Order | customers-who-never-order.sql | O(n^2) | O(1) | Easy | |
| Department Highest Salary | department-highest-salary.sql | O(n^2) | O(n) | Medium | |
| Department Top Three Salaries | department-top-three-salaries.sql | O(n^2) | O(n) | Hard | |
| Duplicate Emails | duplicate-emails.sql | O(n^2) | O(n) | Easy | |
| Employees Earning More Than Their Managers | employees-earning-more-than-their-managers.sql | O(n^2) | O(1) | Easy | |
| Nth Highest Salary | nth-highest-salary.sql | O(n^2) | O(n) | Medium | |
| Rank Scores | rank-scores.sql | O(n^2) | O(n) | Medium | |
| Second Highest Salary | second-highest-salary.sql | O(n) | O(1) | Easy |