LeetCode Knowledge Graph 🎯 — Kernels → Patterns → Problems¶

2025-12-262026-01-04

How to read this map
API Kernel = reusable “engine” (mental + code machine)
Pattern = a specific invariant/state style on top of the kernel
LeetCode {number} = practice anchor (titles auto-added later)
= to-do, [x] = mastered
Primary learning loop
Learn kernel invariant → memorize 1 template → solve 3 problems → refactor template → repeat
Rule of thumb: each element enters/exits state at most once ⇒ aim for \(O(n)\) when possible

⚡ The 4 “Superhighways” (most ROI for interviews)¶

Two Pointers Universe → elimination by monotonic movement
Sliding Window Universe → window state machine with invariant
Backtracking Universe → reversible exploration (choose/explore/unchoose)
Merge / Heap / Partition Universe → ordering + selection primitives

🧠 Kernel 1: `SubstringSlidingWindow` (Window State Machine)¶

Kernel summary: 1D window with dynamic invariant; each element enters/exits ≤ 1 time ⇒ often \(O(n)\)
Window strategies
Maximize: expand R, shrink L only when invalid
Minimize: expand R until valid, shrink L while valid
Fixed size: maintain exact length k
Pattern comparison table 📚

Pattern	Invariant	State	Window	Goal	Anchor Problems
unique	all chars unique	last index map	variable	maximize	`[LeetCode 3 - Longest Substring Without Repeating Characters](https://leetcode.com/problems/longest-substring-without-repeating-characters/description/) · [Solution](https://github.com/lufftw/neetcode/blob/main/solutions/0003_longest_substring_without_repeating_characters.py)`
at_most_k_distinct	distinct ≤ K	freq map	variable	maximize	`[LeetCode 340 - Longest Substring with At Most K Distinct Characters](https://leetcode.com/problems/longest-substring-with-at-most-k-distinct-characters/description/) · [Solution](https://github.com/lufftw/neetcode/blob/main/solutions/0340_longest_substring_with_at_most_k_distinct.py)`
freq_cover	cover required counts	need/have + satisfied	variable	minimize/collect	`[LeetCode 76 - Minimum Window Substring](https://leetcode.com/problems/minimum-window-substring/description/) · [Solution](https://github.com/lufftw/neetcode/blob/main/solutions/0076_minimum_window_substring.py)`, `[LeetCode 438 - Find All Anagrams in a String](https://leetcode.com/problems/find-all-anagrams-in-a-string/description/) · [Solution](https://github.com/lufftw/neetcode/blob/main/solutions/0438_find_all_anagrams_in_a_string.py)`, `[LeetCode 567 - Permutation in String](https://leetcode.com/problems/permutation-in-string/description/) · [Solution](https://github.com/lufftw/neetcode/blob/main/solutions/0567_permutation_in_string.py)`
cost_bounded	sum ≥ target (or ≤ budget)	integer sum	variable	minimize/maximize	`[LeetCode 209 - Minimum Size Subarray Sum](https://leetcode.com/problems/minimum-size-subarray-sum/description/) · [Solution](https://github.com/lufftw/neetcode/blob/main/solutions/0209_minimum_size_subarray_sum.py)`

Pattern: sliding_window_unique
🎯 invariant: “no duplicates in [L,R]”
trick: jump-left using last seen index (no while loop)
[LeetCode 3 - Longest Substring Without Repeating Characters](https://leetcode.com/problems/longest-substring-without-repeating-characters/description/) · [Solution](https://github.com/lufftw/neetcode/blob/main/solutions/0003_longest_substring_without_repeating_characters.py)
Pattern: sliding_window_at_most_k_distinct
🎯 invariant: “distinct count ≤ K”
state: freq, remove keys at 0
[LeetCode 340 - Longest Substring with At Most K Distinct Characters](https://leetcode.com/problems/longest-substring-with-at-most-k-distinct-characters/description/) · [Solution](https://github.com/lufftw/neetcode/blob/main/solutions/0340_longest_substring_with_at_most_k_distinct.py)
Pattern: sliding_window_freq_cover
🎯 invariant: “window satisfies all required frequencies”
two modes:
- minimize window: [LeetCode 76 - Minimum Window Substring](https://leetcode.com/problems/minimum-window-substring/description/) · [Solution](https://github.com/lufftw/neetcode/blob/main/solutions/0076_minimum_window_substring.py)
- fixed window exact match / collect positions: [LeetCode 567 - Permutation in String](https://leetcode.com/problems/permutation-in-string/description/) · [Solution](https://github.com/lufftw/neetcode/blob/main/solutions/0567_permutation_in_string.py), [LeetCode 438 - Find All Anagrams in a String](https://leetcode.com/problems/find-all-anagrams-in-a-string/description/) · [Solution](https://github.com/lufftw/neetcode/blob/main/solutions/0438_find_all_anagrams_in_a_string.py)
[LeetCode 76 - Minimum Window Substring](https://leetcode.com/problems/minimum-window-substring/description/) · [Solution](https://github.com/lufftw/neetcode/blob/main/solutions/0076_minimum_window_substring.py)
[LeetCode 567 - Permutation in String](https://leetcode.com/problems/permutation-in-string/description/) · [Solution](https://github.com/lufftw/neetcode/blob/main/solutions/0567_permutation_in_string.py)
[LeetCode 438 - Find All Anagrams in a String](https://leetcode.com/problems/find-all-anagrams-in-a-string/description/) · [Solution](https://github.com/lufftw/neetcode/blob/main/solutions/0438_find_all_anagrams_in_a_string.py)
Pattern: sliding_window_cost_bounded
🎯 invariant: numeric constraint (often assumes positives for monotonic shrink)
[LeetCode 209 - Minimum Size Subarray Sum](https://leetcode.com/problems/minimum-size-subarray-sum/description/) · [Solution](https://github.com/lufftw/neetcode/blob/main/solutions/0209_minimum_size_subarray_sum.py)
Data structures you’ll feel
hash_map / counter, sometimes arrays of size 26

🧭 Kernel 2: `TwoPointersTraversal` (Eliminate Search Space)¶

Kernel summary: two indices move under a proof-based rule; once moved, never reconsidered
Sub-worlds
Opposite pointers (two-end squeeze)
Same-direction writer (in-place filter/compact)
Dedup enumeration (sorted + skip duplicates)
Two pointers “shape” table

Shape	Init	Movement	Invariant	Typical Time	Anchor Problems
Opposite search	`l=0,r=n-1`	move based on comparison	answer inside [l,r]	\(O(n)\)	`[LeetCode 1 - Two Sum](https://leetcode.com/problems/two-sum/description/) · [Solution](https://github.com/lufftw/neetcode/blob/main/solutions/0001_two_sum.py)`, `LeetCode 167` (related), `[LeetCode 125 - Valid Palindrome](https://leetcode.com/problems/valid-palindrome/description/) · [Solution](https://github.com/lufftw/neetcode/blob/main/solutions/0125_valid_palindrome.py)`
Opposite maximize	`l=0,r=n-1`	move limiting side	best seen so far	\(O(n)\)	`[LeetCode 11 - Container With Most Water](https://leetcode.com/problems/container-with-most-water/description/) · [Solution](https://github.com/lufftw/neetcode/blob/main/solutions/0011_container_with_most_water.py)`
Same-direction writer	`write=0, read=0`	read always, write on keep	`a[0:write]` valid	\(O(n)\)	`[LeetCode 26 - Remove Duplicates from Sorted Array](https://leetcode.com/problems/remove-duplicates-from-sorted-array/description/) · [Solution](https://github.com/lufftw/neetcode/blob/main/solutions/0026_remove_duplicates_from_sorted_array.py)`, `[LeetCode 27 - Remove Element](https://leetcode.com/problems/remove-element/description/) · [Solution](https://github.com/lufftw/neetcode/blob/main/solutions/0027_remove_element.py)`, `[LeetCode 283 - Move Zeroes](https://leetcode.com/problems/move-zeroes/description/) · [Solution](https://github.com/lufftw/neetcode/blob/main/solutions/0283_move_zeroes.py)`, `[LeetCode 80 - Remove Duplicates from Sorted Array II](https://leetcode.com/problems/remove-duplicates-from-sorted-array-ii/description/) · [Solution](https://github.com/lufftw/neetcode/blob/main/solutions/0080_remove_duplicates_from_sorted_array_ii.py)`
Sorted tuple enum	outer i + inner l/r	skip duplicates	uniqueness by ordering	\(O(n^2)\)	`[LeetCode 15 - 3Sum](https://leetcode.com/problems/3sum/description/) · [Solution](https://github.com/lufftw/neetcode/blob/main/solutions/0015_3sum.py)`, `[LeetCode 16 - 3Sum Closest](https://leetcode.com/problems/3sum-closest/description/) · [Solution](https://github.com/lufftw/neetcode/blob/main/solutions/0016_3sum_closest.py)`

Pattern: two_pointer_opposite
🎯 invariant: sorted or monotonic structure ⇒ move pointer that can fix mismatch
[LeetCode 1 - Two Sum](https://leetcode.com/problems/two-sum/description/) · [Solution](https://github.com/lufftw/neetcode/blob/main/solutions/0001_two_sum.py) (often hash map; but opposite-pointer variant when sorted / after sort)
Pattern: two_pointer_opposite_maximize
🎯 invariant: moving the smaller side can only improve potential max
[LeetCode 11 - Container With Most Water](https://leetcode.com/problems/container-with-most-water/description/) · [Solution](https://github.com/lufftw/neetcode/blob/main/solutions/0011_container_with_most_water.py)
Pattern: two_pointer_opposite_palindrome
🎯 invariant: characters must mirror; skip non-alnum if needed
[LeetCode 125 - Valid Palindrome](https://leetcode.com/problems/valid-palindrome/description/) · [Solution](https://github.com/lufftw/neetcode/blob/main/solutions/0125_valid_palindrome.py)
[LeetCode 680 - Valid Palindrome II](https://leetcode.com/problems/valid-palindrome-ii/description/) · [Solution](https://github.com/lufftw/neetcode/blob/main/solutions/0680_valid_palindrome_ii.py)
Pattern: two_pointer_writer_dedup
🎯 invariant: prefix [0:write) is deduped
[LeetCode 26 - Remove Duplicates from Sorted Array](https://leetcode.com/problems/remove-duplicates-from-sorted-array/description/) · [Solution](https://github.com/lufftw/neetcode/blob/main/solutions/0026_remove_duplicates_from_sorted_array.py)
[LeetCode 80 - Remove Duplicates from Sorted Array II](https://leetcode.com/problems/remove-duplicates-from-sorted-array-ii/description/) · [Solution](https://github.com/lufftw/neetcode/blob/main/solutions/0080_remove_duplicates_from_sorted_array_ii.py)
Pattern: two_pointer_writer_remove
🎯 invariant: prefix [0:write) contains kept elements
[LeetCode 27 - Remove Element](https://leetcode.com/problems/remove-element/description/) · [Solution](https://github.com/lufftw/neetcode/blob/main/solutions/0027_remove_element.py)
Pattern: two_pointer_writer_compact
🎯 invariant: all non-zero moved forward; fill remainder
[LeetCode 283 - Move Zeroes](https://leetcode.com/problems/move-zeroes/description/) · [Solution](https://github.com/lufftw/neetcode/blob/main/solutions/0283_move_zeroes.py)
Pattern: two_pointer_three_sum
🎯 invariant: fix i, then two-sum with l/r; dedup by skipping equals
[LeetCode 15 - 3Sum](https://leetcode.com/problems/3sum/description/) · [Solution](https://github.com/lufftw/neetcode/blob/main/solutions/0015_3sum.py)
[LeetCode 16 - 3Sum Closest](https://leetcode.com/problems/3sum-closest/description/) · [Solution](https://github.com/lufftw/neetcode/blob/main/solutions/0016_3sum_closest.py)

🧩 Kernel 3: `FastSlowPointers` (Cycle Physics)¶

Kernel summary: Floyd’s algorithm; detect cycle + locate entry; \(O(n)\) time, \(O(1)\) space
Patterns
fast_slow_cycle_detect → phase 1
- [LeetCode 141 - Linked List Cycle](https://leetcode.com/problems/linked-list-cycle/description/) · [Solution](https://github.com/lufftw/neetcode/blob/main/solutions/0141_linked_list_cycle.py)
fast_slow_cycle_start → phase 2
- [LeetCode 142 - Linked List Cycle II](https://leetcode.com/problems/linked-list-cycle-ii/description/) · [Solution](https://github.com/lufftw/neetcode/blob/main/solutions/0142_linked_list_cycle_ii.py)
fast_slow_midpoint
- [LeetCode 876 - Middle of the Linked List](https://leetcode.com/problems/middle-of-the-linked-list/description/) · [Solution](https://github.com/lufftw/neetcode/blob/main/solutions/0876_middle_of_the_linked_list.py)
fast_slow_implicit_cycle (sequence defined by function)
- [LeetCode 202 - Happy Number](https://leetcode.com/problems/happy-number/description/) · [Solution](https://github.com/lufftw/neetcode/blob/main/solutions/0202_happy_number.py)
Interview punchline
“If there’s a loop, fast gains 1 step per iteration inside the cycle.”

🧱 Kernel 4: `BacktrackingExploration` (Reversible Search)¶

🔀 Kernel 5: `MergeSortedSequences` + `KWayMerge` (Ordering Pipelines)¶

Kernel summary
merge-2: two pointers, \(O(m+n)\)
merge-k: heap (\(O(N \log k)\)) or divide&conquer (\(O(N \log k)\) with better constants/cache)
Patterns
merge_two_sorted_lists
- [LeetCode 21 - Merge Two Sorted Lists](https://leetcode.com/problems/merge-two-sorted-lists/description/) · [Solution](https://github.com/lufftw/neetcode/blob/main/solutions/0021_merge_two_sorted_lists.py)
merge_two_sorted_arrays
- [LeetCode 88 - Merge Sorted Array](https://leetcode.com/problems/merge-sorted-array/description/) · [Solution](https://github.com/lufftw/neetcode/blob/main/solutions/0088_merge_sorted_array.py)
merge_sorted_from_ends
- [LeetCode 977 - Squares of a Sorted Array](https://leetcode.com/problems/squares-of-a-sorted-array/description/) · [Solution](https://github.com/lufftw/neetcode/blob/main/solutions/0977_squares_of_a_sorted_array.py)
merge_k_sorted_heap / merge_k_sorted_divide
- [LeetCode 23 - Merge k Sorted Lists](https://leetcode.com/problems/merge-k-sorted-lists/description/) · [Solution](https://github.com/lufftw/neetcode/blob/main/solutions/0023_merge_k_sorted_lists.py)
Architect lens
Heap merge = “online stream” friendly
Divide&conquer merge = “batch + cache locality” friendly

🧨 Kernel 6: `TwoPointerPartition` (Partition as a Primitive)¶

Kernel summary: in-place region partitioning; foundation for quickselect & Dutch flag
Patterns
dutch_flag_partition
- [LeetCode 75 - Sort Colors](https://leetcode.com/problems/sort-colors/description/) · [Solution](https://github.com/lufftw/neetcode/blob/main/solutions/0075_sort_colors.py)
two_way_partition
- [LeetCode 905 - Sort Array By Parity](https://leetcode.com/problems/sort-array-by-parity/description/) · [Solution](https://github.com/lufftw/neetcode/blob/main/solutions/0905_sort_array_by_parity.py)
- [LeetCode 922 - Sort Array By Parity II](https://leetcode.com/problems/sort-array-by-parity-ii/description/) · [Solution](https://github.com/lufftw/neetcode/blob/main/solutions/0922_sort_array_by_parity_ii.py)
quickselect_partition
- pairs naturally with Top-K / Kth
Complexities
Partition pass: \(O(n)\), \(O(1)\) extra space

🏔️ Kernel 7: `HeapTopK` (Selection & Streaming)¶

Kernel summary: keep best K using heap; or find kth element
Patterns
heap_kth_element
- [LeetCode 215 - Kth Largest Element in an Array](https://leetcode.com/problems/kth-largest-element-in-an-array/description/) · [Solution](https://github.com/lufftw/neetcode/blob/main/solutions/0215_kth_largest_element_in_an_array.py)
Engineering note
For large n, quickselect average \(O(n)\); heap \(O(n \log k)\) but stable & incremental

🌊 Kernel 8: `GridBFSMultiSource` (Wavefront Propagation)¶

Kernel summary: multi-source BFS; shortest time/steps in unweighted grid
Pattern
grid_bfs_propagation
- [LeetCode 994 - Rotting Oranges](https://leetcode.com/problems/rotting-oranges/description/) · [Solution](https://github.com/lufftw/neetcode/blob/main/solutions/0994_rotting_oranges.py)
Invariant
queue holds the current frontier; each layer = +1 minute/step

🧪 “Combo Moves” (patterns that fuse)¶

Sliding Window + Hash Map: [LeetCode 3 - Longest Substring Without Repeating Characters](https://leetcode.com/problems/longest-substring-without-repeating-characters/description/) · [Solution](https://github.com/lufftw/neetcode/blob/main/solutions/0003_longest_substring_without_repeating_characters.py), [LeetCode 76 - Minimum Window Substring](https://leetcode.com/problems/minimum-window-substring/description/) · [Solution](https://github.com/lufftw/neetcode/blob/main/solutions/0076_minimum_window_substring.py), [LeetCode 340 - Longest Substring with At Most K Distinct Characters](https://leetcode.com/problems/longest-substring-with-at-most-k-distinct-characters/description/) · [Solution](https://github.com/lufftw/neetcode/blob/main/solutions/0340_longest_substring_with_at_most_k_distinct.py), [LeetCode 438 - Find All Anagrams in a String](https://leetcode.com/problems/find-all-anagrams-in-a-string/description/) · [Solution](https://github.com/lufftw/neetcode/blob/main/solutions/0438_find_all_anagrams_in_a_string.py), [LeetCode 567 - Permutation in String](https://leetcode.com/problems/permutation-in-string/description/) · [Solution](https://github.com/lufftw/neetcode/blob/main/solutions/0567_permutation_in_string.py)
Two Pointers + Sorting + Dedup: [LeetCode 15 - 3Sum](https://leetcode.com/problems/3sum/description/) · [Solution](https://github.com/lufftw/neetcode/blob/main/solutions/0015_3sum.py), [LeetCode 16 - 3Sum Closest](https://leetcode.com/problems/3sum-closest/description/) · [Solution](https://github.com/lufftw/neetcode/blob/main/solutions/0016_3sum_closest.py)
Partition + Heap/Quickselect: [LeetCode 215 - Kth Largest Element in an Array](https://leetcode.com/problems/kth-largest-element-in-an-array/description/) · [Solution](https://github.com/lufftw/neetcode/blob/main/solutions/0215_kth_largest_element_in_an_array.py)
Backtracking + DP precompute: [LeetCode 131 - Palindrome Partitioning](https://leetcode.com/problems/palindrome-partitioning/description/) · [Solution](https://github.com/lufftw/neetcode/blob/main/solutions/0131_palindrome_partitioning.py) (palindrome table)
Merge + Binary Search on answer: [LeetCode 4 - Median of Two Sorted Arrays](https://leetcode.com/problems/median-of-two-sorted-arrays/description/) · [Solution](https://github.com/lufftw/neetcode/blob/main/solutions/0004_median_of_two_sorted_arrays.py) (two sorted arrays median)

🧭 Micro-Roadmaps (fast, high-signal)¶

Sliding Window Mastery (sliding_window_path)
[LeetCode 3 - Longest Substring Without Repeating Characters](https://leetcode.com/problems/longest-substring-without-repeating-characters/description/) · [Solution](https://github.com/lufftw/neetcode/blob/main/solutions/0003_longest_substring_without_repeating_characters.py) → [ ] [LeetCode 340 - Longest Substring with At Most K Distinct Characters](https://leetcode.com/problems/longest-substring-with-at-most-k-distinct-characters/description/) · [Solution](https://github.com/lufftw/neetcode/blob/main/solutions/0340_longest_substring_with_at_most_k_distinct.py) → [ ] [LeetCode 209 - Minimum Size Subarray Sum](https://leetcode.com/problems/minimum-size-subarray-sum/description/) · [Solution](https://github.com/lufftw/neetcode/blob/main/solutions/0209_minimum_size_subarray_sum.py) → [ ] [LeetCode 567 - Permutation in String](https://leetcode.com/problems/permutation-in-string/description/) · [Solution](https://github.com/lufftw/neetcode/blob/main/solutions/0567_permutation_in_string.py) → [ ] [LeetCode 438 - Find All Anagrams in a String](https://leetcode.com/problems/find-all-anagrams-in-a-string/description/) · [Solution](https://github.com/lufftw/neetcode/blob/main/solutions/0438_find_all_anagrams_in_a_string.py) → [ ] [LeetCode 76 - Minimum Window Substring](https://leetcode.com/problems/minimum-window-substring/description/) · [Solution](https://github.com/lufftw/neetcode/blob/main/solutions/0076_minimum_window_substring.py)
Two Pointers Mastery (two_pointers_path)
[LeetCode 26 - Remove Duplicates from Sorted Array](https://leetcode.com/problems/remove-duplicates-from-sorted-array/description/) · [Solution](https://github.com/lufftw/neetcode/blob/main/solutions/0026_remove_duplicates_from_sorted_array.py) → [ ] [LeetCode 27 - Remove Element](https://leetcode.com/problems/remove-element/description/) · [Solution](https://github.com/lufftw/neetcode/blob/main/solutions/0027_remove_element.py) → [ ] [LeetCode 283 - Move Zeroes](https://leetcode.com/problems/move-zeroes/description/) · [Solution](https://github.com/lufftw/neetcode/blob/main/solutions/0283_move_zeroes.py) → [ ] [LeetCode 11 - Container With Most Water](https://leetcode.com/problems/container-with-most-water/description/) · [Solution](https://github.com/lufftw/neetcode/blob/main/solutions/0011_container_with_most_water.py) → [ ] [LeetCode 125 - Valid Palindrome](https://leetcode.com/problems/valid-palindrome/description/) · [Solution](https://github.com/lufftw/neetcode/blob/main/solutions/0125_valid_palindrome.py) → [ ] [LeetCode 15 - 3Sum](https://leetcode.com/problems/3sum/description/) · [Solution](https://github.com/lufftw/neetcode/blob/main/solutions/0015_3sum.py)
Backtracking Core
[LeetCode 78 - Subsets](https://leetcode.com/problems/subsets/description/) · [Solution](https://github.com/lufftw/neetcode/blob/main/solutions/0078_subsets.py) → [ ] [LeetCode 77 - Combinations](https://leetcode.com/problems/combinations/description/) · [Solution](https://github.com/lufftw/neetcode/blob/main/solutions/0077_combinations.py) → [ ] [LeetCode 46 - Permutations](https://leetcode.com/problems/permutations/description/) · [Solution](https://github.com/lufftw/neetcode/blob/main/solutions/0046_permutations.py) → [ ] [LeetCode 39 - Combination Sum](https://leetcode.com/problems/combination-sum/description/) · [Solution](https://github.com/lufftw/neetcode/blob/main/solutions/0039_combination_sum.py) → [ ] [LeetCode 40 - Combination Sum II](https://leetcode.com/problems/combination-sum-ii/description/) · [Solution](https://github.com/lufftw/neetcode/blob/main/solutions/0040_combination_sum_ii.py) → [ ] [LeetCode 131 - Palindrome Partitioning](https://leetcode.com/problems/palindrome-partitioning/description/) · [Solution](https://github.com/lufftw/neetcode/blob/main/solutions/0131_palindrome_partitioning.py) → [ ] [LeetCode 51 - N-Queens](https://leetcode.com/problems/n-queens/description/) · [Solution](https://github.com/lufftw/neetcode/blob/main/solutions/0051_n_queens.py)
BFS Wavefront
[LeetCode 994 - Rotting Oranges](https://leetcode.com/problems/rotting-oranges/description/) · [Solution](https://github.com/lufftw/neetcode/blob/main/solutions/0994_rotting_oranges.py)

LeetCode Knowledge Graph 🎯 — Kernels → Patterns → Problems¶

⚡ The 4 “Superhighways” (most ROI for interviews)¶

🧠 Kernel 1: SubstringSlidingWindow (Window State Machine)¶

🧭 Kernel 2: TwoPointersTraversal (Eliminate Search Space)¶

🧩 Kernel 3: FastSlowPointers (Cycle Physics)¶

🧱 Kernel 4: BacktrackingExploration (Reversible Search)¶

🔀 Kernel 5: MergeSortedSequences + KWayMerge (Ordering Pipelines)¶

🧨 Kernel 6: TwoPointerPartition (Partition as a Primitive)¶

🏔️ Kernel 7: HeapTopK (Selection & Streaming)¶

🌊 Kernel 8: GridBFSMultiSource (Wavefront Propagation)¶

🧪 “Combo Moves” (patterns that fuse)¶

🧭 Micro-Roadmaps (fast, high-signal)¶

✅ Progress Board (printable)¶

🧠 Kernel 1: `SubstringSlidingWindow` (Window State Machine)¶

🧭 Kernel 2: `TwoPointersTraversal` (Eliminate Search Space)¶

🧩 Kernel 3: `FastSlowPointers` (Cycle Physics)¶

🧱 Kernel 4: `BacktrackingExploration` (Reversible Search)¶

🔀 Kernel 5: `MergeSortedSequences` + `KWayMerge` (Ordering Pipelines)¶

🧨 Kernel 6: `TwoPointerPartition` (Partition as a Primitive)¶

🏔️ Kernel 7: `HeapTopK` (Selection & Streaming)¶

🌊 Kernel 8: `GridBFSMultiSource` (Wavefront Propagation)¶