The Blind 75 Leetcode Series: The Final Trimester Review
Finally! After more than a year from our second trimester, we’ve finally finished the rest of the problems! I apologize for my slowness. But after all, we are done!
In the last 3rd of the set, we’ve visited these problems
52. Kth Smallest Element in a BST
53. Lowest Common Ancestor of a Binary Search Tree
54. Lowest Common Ancestor of a Binary Tree
55. Product of Array Except Self
56. Valid Anagram
57. Meeting Rooms
58. Meeting Rooms II
59. Graph Valid Tree
60. Missing Number
61. Alien Dictionary
63. Find Median from Data Stream
64. Longest Increasing Subsequence
65. Coin Change
66. Number of Connected Components in an Undirected Graph
67. Counting Bits
70. Pacific Atlantic Water Flow
71. Longest Repeating Character Replacement
Types of Problem
Then we look at the type of problems:
- Trees
- 51. Invert Binary Tree
- 52. Kth Smallest Element in a BST
- 53. Lowest Common Ancestor of a Binary Search Tree
- 54. Lowest Common Ancestor of a Binary Tree
- 59. Graph Valid Tree
- 73. Serialize and Deserialize BST
- 74. Subtree of Another Tree
- Array/String
- 55. Product of Array Except Self
- 56. Valid Anagram
- 57. Meeting Rooms
- 58. Meeting Rooms II
- 60. Missing Number
- 61. Alien Dictionary
- 62. Encode and Decode Strings
- 63. Find Median from Data Stream
- 64. Longest Increasing Subsequence
- 65. Coin Change
- 68. Top K Frequent Elements
- 71. Longest Repeating Character Replacement
- 72. Non-overlapping Intervals
- 75. Palindromic Substrings
- 76. Longest Common Subsequence
- Graph
- 66. Number of Connected Components in an Undirected Graph
- Bits
- 67. Counting Bits
- Math
- 69. Sum of Two Integers
- 65. Coin Change
- Matrix
- 70. Pacific Atlantic Water Flow
The array problems still dominate the categories. This is something we can expect. There are just so many things we can do with arrays, and usually the problems are simple enough that candidates don’t have to take too much time to understand.
Types of Question Asks
- Trees
- 51. Invert Binary Tree
- 53. Lowest Common Ancestor of a Binary Search Tree
- 54. Lowest Common Ancestor of a Binary Tree
- 59. Graph Valid Tree
- 73. Serialize and Deserialize BST
- 74. Subtree of Another Tree
- Search
- 52. Kth Smallest Element in a BST
- 60. Missing Number
- 63. Find Median from Data Stream
- 68. Top K Frequent Elements
- 66. Number of Connected Components in an Undirected Graph
- 70. Pacific Atlantic Water Flow
- Intervals
- 57. Meeting Rooms
- 58. Meeting Rooms II
- 72. Non-overlapping Intervals
- String
- 56. Valid Anagram
- 61. Alien Dictionary
- 62. Encode and Decode Strings
- Math
- 55. Product of Array Except Self
- 67. Counting Bits
- 69. Sum of Two Integers
- 65. Coin Change
- Subsequence
- 64. Longest Increasing Subsequence
- 71. Longest Repeating Character Replacement
- 75. Palindromic Substrings
- 76. Longest Common Subsequence
Techniques
DFS / BFS
- 51. Invert Binary Tree
- 70. Pacific Atlantic Water Flow
- 73. Serialize and Deserialize BST
- 74. Subtree of Another Tree
Binary Search
- 52. Kth Smallest Element in a BST
- 53. Lowest Common Ancestor of a Binary Search Tree
- 54. Lowest Common Ancestor of a Binary Tree
Dynamic Programming
- 55. Product of Array Except Self
- 64. Longest Increasing Subsequence
- 65. Coin Change
- 67. Counting Bits
- 76. Longest Common Subsequence
Hash Map
- 56. Valid Anagram
- 60. Missing Number
Sort
- 57. Meeting Rooms
- 58. Meeting Rooms II
- 72. Non-overlapping Intervals
Graph (Traversal)
- 59. Graph Valid Tree
- 66. Number of Connected Components in an Undirected Graph
Topological Sort
- 61. Alien Dictionary
String Encoding/Decoding
- 62. Encode and Decode Strings
Heap (Priority Queue)
- 63. Find Median from Data Stream
Bucket Sort
- 68. Top K Frequent Elements
Bit Manipulation
- 69. Sum of Two Integers
Sliding Window
- 71.Longest Repeating Character Replacement
Two Pointers
- 75. Palindromic Substrings
Boy….. this set is everywhere…… we still see a good stack of DFS/BFS problems as well as dynamic programming. Sorting, in different ways, take a lot of places as well.
From the list, I still think the tree problems are most popular these days as well as any kind of problems including sorting. DP…… still around but I don’t see them as well, at least in my company.
That doesn’t mean you shouldn’t study these, but there are definitely ranking in terms of frequency, not just Blind 75, but these types of Leetcode problems in general.
Now that we are finally done with the list, we should have some good understanding of what topics we are expecting, and approaches we should take.
Granted, there are more than one way to approach a problem, but we should see the patterns of these. As top tech companies make these Leetcode problems harder and harder, the problem becomes a word game. How to translate the words into coding languages/technics becomes essential on top of knowing how to solve a problem.
It’s unfortunate that the interview process becomes like this. Most of people I know hate this, but this is the game we play. I don’t see this changing any time soon.
So for now, study up! Good luck with your job searching process! I hope this series helps you even just a little. If it does even help you to understand just one problem, then it did its job.