LeetCode 
My solutions to problems on LeetCode (https://leetcode.com/) using Java or Ruby sometimes.
Every solution has its corresponding question number, name, general idea to solve the problem and different methods used written in the top comment.
Current Solutions
Array
| Status |
No. |
Title |
Language |
Time |
Space |
Note |
| ✅ |
1 |
Two Sum |
Java/Ruby |
O(n) |
O(n) |
HashMap |
| ✅ |
122 |
Best Time to Buy and Sell Stock II |
Java |
O(n) |
O(1) |
Accumulation of profit, Peak-valley is overkill but can be useful sometime. |
| ✅ |
136 |
Single Number |
Java |
O(n) |
O(1) |
XOR is always the trick! |
| ✅ |
283 |
Move Zeroes |
Java |
O(n) |
O(1) |
Two pointers, best & worst cases help understand |
| ✅ |
412 |
FizzBuzz |
Java |
O(n) |
O(n) |
LinkedList |
Math
| Status |
No. |
Title |
Language |
Time |
Space |
Note |
| ✅ |
171 |
Excel Sheet Column Number |
Java |
O(n) |
O(1) |
Base 26 calculation |
List
| Status |
No. |
Title |
Language |
Time |
Space |
Note |
| ✅ |
237 |
Delete Node in a Linked List |
O(1) |
O(1) |
Java |
Without access to the previous node, replace current node with next node and delete the next node |
String
| Status |
No. |
Title |
Language |
Time |
Space |
Note |
| ✅ |
344 |
Reverse String |
Java |
O(n) |
O(n) |
Char array and String.valueOf() |
| ✅ |
387 |
First Unique Character in a String |
Java |
O(n) |
O(1) |
Bit vector counting the frequency of char |
Tree
| Status |
No. |
Title |
Language |
Time |
Space |
Note |
| ✅ |
104 |
Maximum Depth of Binary Tree |
Java |
O(n) |
O(n) |
With/without instance variable Top-bottom tree traversal |
Bit Manipulation
| Status |
No. |
Title |
Language |
Time |
Space |
Note |
| ✅ |
371 |
Sum of Two Integers |
Java |
O(n) |
O(n) |
Sum without carry by ^, carry by & |
HashSet, HashTable
| No. |
Title |
Language |
Time |
Space |
Note |
| 136 |
Single Number |
Java |
|
|
HashSet |
| 137 |
Single Number II |
Java |
|
|
HashSet |
| 217 |
Contains Duplicate |
Java/Ruby |
|
|
HashSet |
| 242 |
Valid Anagram |
Java |
|
|
HashMap |
Binary Search
| No. |
Title |
Language |
Note |
| 278 |
First Bad Version |
Java |
|
Binary Tree
| No. |
Title |
Language |
Note |
| 226 |
Invert Binary Tree |
Java |
|
Two Pointers
| No. |
Title |
Language |
Note |
| 26 |
Remove Duplicates from Sorted Array |
Java |
|
| 27 |
Remove Element |
Java |
|
Not Yet Categorised
| No. |
Title |
Language |
Note |
| 198 |
House Robber |
Java |
|
| 338 |
Counting Bits |
Java/Ruby |
|
| 239 |
Sliding Window Maximum |
Java |
|
| 344 |
Reverse String |
Java |
|
| 347 |
Top K Frequent Elements |
Java |
|
