Backtracking — NeetCode 250

This is a fresh, pattern-first study track for 15 core Backtracking problems. Read the foundation once, then work the problems in order. The aim is to recognize the decision tree before writing code.

Start here

1. 00 - Backtracking Foundations
2. 01 - Subsets and Duplicates
3. 02 - Combinations and Targets
4. 03 - Permutations
5. 04 - Strings and Grids
6. 05 - Constraint Search

The 15-problem track

#	Problem	Main pattern	Note
1	Sum of All Subsets XOR Total	Include / exclude with an accumulator	01 - Subsets and Duplicates
2	Subsets	Enumerate every subset	01 - Subsets and Duplicates
3	Subsets II	Subsets with duplicates	01 - Subsets and Duplicates
4	Combination Sum	Target; reuse allowed	02 - Combinations and Targets
5	Combination Sum II	Target; use once; deduplicate	02 - Combinations and Targets
6	Combinations	Choose k increasing values	02 - Combinations and Targets
7	Permutations	Arrange unused values	03 - Permutations
8	Permutations II	Arrange values with frequencies	03 - Permutations
9	Generate Parentheses	Build a valid constrained sequence	04 - Strings and Grids
10	Letter Combinations of a Phone Number	One choice per position	04 - Strings and Grids
11	Palindrome Partitioning	Choose the next valid cut	04 - Strings and Grids
12	Word Search	Grid DFS; path-local visited state	04 - Strings and Grids
13	N-Queens	Place under constraints	05 - Constraint Search
14	N-Queens II	Count constrained placements	05 - Constraint Search
15	Matchsticks to Square	Assign items to equal buckets	05 - Constraint Search

How to use each problem note

Before looking at the solution, answer these five prompts aloud:

1. What does one DFS call mean?
2. What is the next decision?
3. Which state is shared and must be undone?
4. When is a partial path impossible?
5. What condition means the answer is complete?

Then write the recurrence from memory. If you get stuck, compare the problem with its nearest neighbor in the same note—not with a memorized full solution.

One-page pattern map

If the prompt says…	Reach for…
“every subset”	start index or include/exclude
“unique” and input has duplicates	sort, then skip equal choices at the same depth
“sum to target”	DFS with remaining target
“use a value again”	recurse with the same index
“use each value once”	recurse from the next index
“every ordering”	choose from unused values
“all valid cuts / strings”	try every next valid piece
“grid path cannot reuse a cell”	mark, explore, restore
“place / assign under rules”	choose a slot, maintain fast constraint sets, prune symmetry

Why this guide covers 15 of NeetCode 250’s 17 Backtracking problems

NeetCode 250 currently labels 17 questions as Backtracking. This guide keeps the 15 where backtracking is the primary pattern to learn and solve.

The two exceptions are intentionally studied elsewhere:

• Partition to K Equal Sum Subsets — use the 1-D DP / bitmask-DP treatment. Although a brute-force search exists, the reusable interview pattern is state compression and memoization.
• Word Break II — use memoized DFS / 1-D DP after mastering ordinary backtracking. Its important idea is caching suffix results, not just exploring a decision tree.

Trie-led Word Search II is another worthwhile follow-on after this core track.