Blind 75 in Python: The Idioms and Library Tools for Each Category

The Blind 75 is short enough to finish in a month, and Python keeps each solution to a few lines, so the remaining risk is the language's own traps: floor division, aliased lists and integers that never overflow. This page goes through the list's categories with the Python tools each one needs, covers the problems where Python behaves differently from other languages, and gives a six-week order. For the list itself, see our Blind 75 guide; for language questions, our Python interview questions.

The list by category

Blind 75 has 19 easy, 49 medium and 7 hard problems, six of them LeetCode Premium. Counts were read from each list's own site data in November 2026. Lists are edited from time to time, so numbers can drift. Grouped by NeetCode's categories:

Problems where Python needs care

• Sum of Two Integers: Python integers have no 32-bit limit, so the carry loop never ends on negative inputs. Mask with 0xFFFFFFFF each round and convert back at the end with a if a <= 0x7FFFFFFF else ~(a ^ 0xFFFFFFFF).
• Number of 1 Bits and Reverse Bits: n.bit_count() (Python 3.10 and later) or bin(n).count('1') are fine to mention, but write the shift loop when asked; Reverse Bits must loop exactly 32 times.
• Encode and Decode Strings (Premium): a length prefix such as f'{len(s)}#{s}' survives any characters, including the delimiter.
• Merge k Sorted Lists: ListNode objects cannot be compared, so push (node.val, i, node) tuples into heapq; the index breaks ties.
• Longest Increasing Subsequence: the O(n log n) version is short with bisect_left on a list of tails.
• Maximum Product Subarray: track both the running maximum and minimum, swapping them when the number is negative.
• Alien Dictionary (Premium): the standard library has graphlib.TopologicalSorter, but interviewers expect Kahn's algorithm with a deque; also check the prefix case, where a longer word comes before its own prefix.
• Meeting Rooms II (Premium): sort by start and keep a min-heap of end times; the heap size at the end is the answer.

Language traps worth knowing

• // floors toward negative infinity, so -7 // 2 is -4; use int(a / b) when a problem wants truncation toward zero.
• [[0] * n] * m creates m references to one row; build grids with [[0] * n for _ in range(m)].
• list.sort() returns None; sorted() returns a new list.
• Slicing copies: s[i:j] inside a dynamic programming loop adds a hidden factor of n.
• Default recursion depth is about 1,000 frames, enough for balanced trees but not for a 10,000-node linked list.
• Comparing small integers with is seems to work and then fails on larger values; always use ==.

A six-week order

1. Week 1: arrays and hashing, two pointers and sliding window (15 problems).
2. Week 2: stack, binary search and linked lists (9).
3. Week 3: trees and tries (14).
4. Week 4: heap, backtracking and graphs (10).
5. Week 5: dynamic programming (12).
6. Week 6: greedy, intervals, math and bits (15), then redo every problem you failed.

After Blind 75, the NeetCode 150 in Python plan adds 75 more problems with the same tools, or switch to the ranked Grind 75 guide if your interview is soon.

Turning a list into interview skill

Any list only helps if the practice transfers to problems you have not seen. These habits make the difference:

1. Time-box every attempt: about 25 minutes for a medium before you read a solution.
2. Keep a log with one line per problem: the pattern, the key idea and the complexity.
3. Redo failed problems after three days, a week and three weeks, without looking at your old code.
4. Explain your approach out loud before and while you code, as you would to an interviewer.
5. In the last two weeks, switch to unseen problems without topic labels.

The patterns most lists are built on are explained in array and string patterns and tree, graph and recursion patterns.

Where CoPilot Interview fits

Finishing a list is not the same as passing an interview: interviewers score how you explain your approach, your trade-offs and your complexity out loud. CoPilot Interview is an AI interview assistant; its free AI mock interview asks coding questions, listens to your spoken explanation and scores it out of ten with a model answer, which is the part a problem list cannot train. The free plan gives 15 minutes a day of live help in sessions of up to 15 minutes, with AI mock interviews included. Online assessments and live coding rounds usually forbid outside help, so practice now and follow your employer's rules on the day.

Disclosure: CoPilot Interview is our product, so weigh what we say about it accordingly.

Frequently asked questions

Is Python the best language for Blind 75?

It gives the shortest solutions, which leaves more interview time for explanation. Any mainstream language is accepted, so choose the one you write most fluently.

Which Blind 75 problems need LeetCode Premium?

Six: Encode and Decode Strings, Graph Valid Tree, Number of Connected Components in an Undirected Graph, Alien Dictionary, and Meeting Rooms I and II.

Why does Sum of Two Integers loop forever in Python?

Python integers grow without limit, so negative numbers never run out of carry bits. Mask with 0xFFFFFFFF and convert the result back to a signed value.

How long does Blind 75 take in Python?

Four to six weeks at two or three problems a day with review is typical; experienced candidates can revise it in two weeks.