Data Types

Absolutely — knowing your core data types inside and out is essential for LeetCode and coding interviews. These are the types you’ll see constantly and will use to build efficient solutions.

Here’s a curated list of the must-know data types for LeetCode — including how to use them, when to choose them, and a one-liner to remember what they’re best at.

🧠 LeetCode Data Types You Should Know (Python)

✅ 1. int – Whole numbers

Used for counting, math, binary, etc.

n = 42

🧪 Use cases:

• Loops, math, binary search, bit manipulation

✅ 2. float – Decimal numbers

Used rarely, but important for precision-sensitive problems.

pi = 3.14

🧪 Watch out for rounding errors.

✅ 3. str – Strings

🔥 High-frequency on LeetCode

s = "leetcode"

🧪 Know:

• s[::-1] – reverse

• s.split() – split by whitespace

• s.isalnum() – alphanumeric check

• ord(c), chr(n) – ASCII value

✅ 4. list – Ordered, mutable collection

🔥 Most used structure in LeetCode

arr = [1, 2, 3]

🧪 Know:

• arr.append(x)

• arr.pop(), arr.pop(0)

• arr[::-1]

• arr.sort() vs sorted(arr)

• Slicing, binary search, sliding window

✅ 5. tuple – Ordered, immutable collection

Used for keys in sets/dicts or returning multiple values.

t = (1, 2)

🧪 Know:

• x, y = t

• Useful as hashable keys: visited[(x, y)] = True

✅ 6. set – Unordered, unique items

🔑 Great for fast lookup and duplicates

s = set([1, 2, 3])

🧪 Know:

• x in s → O(1)

• set(list) removes duplicates

• Set operations: union, intersection, difference

✅ 7. dict – Key-value pairs

🔥 Critical for hash maps / fast lookups

d = {"a": 1, "b": 2}

🧪 Know:

• d.get(k, default)

• defaultdict(list)

• Frequency count: Counter(s)

• Keys/values/items iteration

✅ 8. collections.deque – Double-ended queue

⚡ Fast append and popleft() → great for BFS

from collections import deque
q = deque([1, 2])
q.append(3)
q.popleft()

✅ 9. heapq / Min Heap (via list)

💡 Use for priority queue, top K elements

import heapq
h = [5, 3, 8]
heapq.heapify(h)
heapq.heappop(h)

🧪 Python only has min-heaps — invert values for max-heap.

✅ 10. collections.Counter – Fast frequency counting

from collections import Counter
c = Counter("aabbcc")

🧪 Useful for:

• Anagram check

• Majority element

• Multiset behavior

🧠 TL;DR: Memorize These for LeetCode

Would you like:

• Anki cards for this?

• Daily drills where you implement key operations from memory?

• A printable reference sheet or PDF?