---
tags: Software Engineer, Leetcode,
---

# Interview Leetcode Notes

> Writing code for Interview != writing code at work/school.

## Common Data Structures

- List, Array, LinkedList
- Map
- Set
- Graph
- Tree
- Binary Tree
- Binary Search Tree
- Stack, Queue, Hash, Heap
- Union Find
- Trie
## Common Algorithm Templates

### Binary Search

begin, end
while begin + 1 < end:
    mid = (begin + end) // 2
    some logic to assign mid to begin or end

- [First Bad Version](https://leetcode.com/problems/first-bad-version/)
- [First & Last Position](https://leetcode.com/problems/find-first-and-last-position-of-element-in-sorted-array/)
- [Peak element](https://leetcode.com/problems/find-peak-element/)
- [All Binary Search problems](https://leetcode.com/problemset/all/?topicSlugs=binary-search&page=1&sorting=W3sic29ydE9yZGVyIjoiREVTQ0VORElORyIsIm9yZGVyQnkiOiJGUkVRVUVOQ1kifV0%3D)

### Two pointer

left, right
while left <= right
     while left <= right and <left's condition>:
         left += 1
     while left <= right and <right's condition>:
         right -= 1

     if left <= right:
         do something (ex. swap left & right)
         left += 1
         right -= 1

- Reverse
- https://leetcode.com/problems/valid-palindrome/
- https://leetcode.com/problems/valid-palindrome-ii/
- Two Sum
- https://leetcode.com/problems/two-sum/
- https://leetcode.com/problems/3sum/
- https://leetcode.com/problems/4sum/
- Partition
- Quick Select

### BFS, topological sort

https://leetcode.com/problems/binary-tree-zigzag-level-order-traversal/

### Binary Tree

https://leetcode.com/problems/binary-tree-inorder-traversal

https://leetcode.com/problems/closest-binary-search-tree-value-ii/solution/

### DFS Combination

https://leetcode.com/problems/combination-sum/
https://leetcode.com/problems/subarray-sum-equals-k/
https://leetcode.com/problems/wildcard-matching/

### DFS Permutation

### Interval

## Python data structures

Map: dict `{}`

`set()`

x = [] # List, Stack
y = list(x)

_Map = {}
_Dict = {}

x_set = set()

from collections import Counter
Counter()

queue

heap

## Java data structures

List

List<Integer> list = new ArrayList<>();
list.add();
list.addAll();
list.get(i)
list.remove(object);
list.remove(index);

Map

Map<Integer, String> map = new HashMap<>();
Map<Integer, String> map = new TreeMap<>();

map.put(key, value);
map.containsKey(key);
map.get(key);
map.getOrDefault(key, defaultValue);
map.remove

Set

Set<Integer> set = new HashSet<>();
set1.addAll(set2); // union
set1.retainAll(set2); // intersection

LinkedList

Stack

Stack<Integer> stack = new Stack<>();
stack.push(1);
stack.pop();
stack.peek();
stack.isEmpty();

Deque<TreeNode> stack = new ArrayDeque<>();

Queue

Queue<Integer> queue = new LinkedList<>();

PriorityQueue

Utilities

Character.isLetterOrDigit()
Character.toLowerCase()
Arrays.sort(list, (a, b) -> a - b); // ascending
Arrays.sort(list, (a, b) -> b - a); // descending
Collections.sort();
Collections.reverse();