# GROKKING NOTES

I liked the way Grokking the coding interview organized problems into learnable patterns. However, the course is expensive and the majority of the time the problems are copy-pasted from leetcode. As the explanations on leetcode are usually just as good, the course really boils down to being a glorified curated list of leetcode problems.

So below I made a list of leetcode problems that are as close to grokking problems as possible.

- [ ] Unchecked
- [x] Checked

## Pattern: Sliding Window

- [ ] <https://leetcode.com/problems/maximum-subarray/> # Close enough

- [ ] <https://leetcode.com/problems/minimum-size-subarray-sum/>
- [ ] <https://leetcode.com/problems/longest-substring-with-at-most-k-distinct-characters/>
- [ ] <https://leetcode.com/problems/fruit-into-baskets/>
- [ ] <https://leetcode.com/problems/longest-substring-without-repeating-characters/>
- [ ] <https://leetcode.com/problems/longest-repeating-character-replacement/>
- [ ] <https://leetcode.com/problems/max-consecutive-ones-iii/>
- [ ] <https://leetcode.com/problems/permutation-in-string/>
- [ ] <https://leetcode.com/problems/find-all-anagrams-in-a-string/>
- [ ] <https://leetcode.com/problems/minimum-window-substring/>
- [ ] <https://leetcode.com/problems/substring-with-concatenation-of-all-words/>

## Pattern: Two Pointers

- [ ] <https://leetcode.com/problems/two-sum/>
- [ ] <https://leetcode.com/problems/remove-duplicates-from-sorted-array/>
- [ ] <https://leetcode.com/problems/squares-of-a-sorted-array/>
- [ ] <https://leetcode.com/problems/3sum/>
- [ ] <https://leetcode.com/problems/3sum-closest/>
- [ ] <https://leetcode.com/problems/3sum-smaller/>
- [ ] <https://leetcode.com/problems/subarray-product-less-than-k/>
- [ ] <https://leetcode.com/problems/sort-colors/>
- [ ] <https://leetcode.com/problems/4sum/>
- [ ] <https://leetcode.com/problems/backspace-string-compare/>
- [ ] <https://leetcode.com/problems/shortest-unsorted-continuous-subarray/>

## Pattern: Fast & Slow pointers

- [ ] <https://leetcode.com/problems/linked-list-cycle/>
- [ ] <https://leetcode.com/problems/linked-list-cycle-ii/>
- [ ] <https://leetcode.com/problems/happy-number/>
- [ ] <https://leetcode.com/problems/middle-of-the-linked-list/>
- [ ] <https://leetcode.com/problems/palindrome-linked-list/>
- [ ] <https://leetcode.com/problems/reorder-list/>
- [ ] <https://leetcode.com/problems/circular-array-loop/>

## Pattern: Merge Intervals

- [ ] <https://leetcode.com/problems/merge-intervals/>
- [ ] <https://leetcode.com/problems/insert-interval/>
- [ ] <https://leetcode.com/problems/interval-list-intersections/>
- [ ] <https://leetcode.com/problems/meeting-rooms-ii/>
- [ ] Could not find equivalent. Given a list of intervals with values, find the peak sum (i.e. if intervals are overlapping, sum their values)
- [ ] <https://leetcode.com/problems/employee-free-time/>

## Pattern: Cyclic Sort

- [ ] Couldn't find equivalent for the first question. The second question below encompasses the first one though. See <https://leetcode.com/problems/missing-number/discuss/859510/C%2B%2B-O(N)-O(1)-using-Cyclic-Sort> for how grokking the coding interview approached these problems. It uses the fact that we can sort the array in O(n) without comparison operators
- [ ] <https://leetcode.com/problems/missing-number/>
- [ ] <https://leetcode.com/problems/find-all-numbers-disappeared-in-an-array/>
- [ ] <https://leetcode.com/problems/find-all-duplicates-in-an-array/>
- [ ] combine <https://leetcode.com/problems/find-the-duplicate-number/> and <https://leetcode.com/problems/missing-number/>
- [ ] <https://leetcode.com/problems/first-missing-positive/>
- [ ] <https://leetcode.com/problems/kth-missing-positive-number/>

## Pattern: In-place Reversal of a LinkedList

- [ ] <https://leetcode.com/problems/reverse-linked-list/>
- [ ] <https://leetcode.com/problems/reverse-linked-list-ii/>
- [ ] <https://leetcode.com/problems/reverse-nodes-in-k-group/>
- [ ] Next question is the same, but alternate each subgroup
- [ ] <https://leetcode.com/problems/rotate-list/>

## Pattern: Tree Breadth First Search

- [ ] <https://leetcode.com/problems/binary-tree-level-order-traversal/>
- [ ] <https://leetcode.com/problems/binary-tree-level-order-traversal-ii/>
- [ ] <https://leetcode.com/problems/binary-tree-zigzag-level-order-traversal/>
- [ ] <https://leetcode.com/problems/minimum-depth-of-binary-tree/>
- [ ] <https://leetcode.com/problems/inorder-successor-in-bst/>  # Close, not exact
- [ ] <https://leetcode.com/problems/populating-next-right-pointers-in-each-node/>  # Close, grokk assumes non-perfect tree
- [ ] Next question is the same, but connect end nodes to the next level instead of null
- [ ] <https://leetcode.com/problems/binary-tree-right-side-view/>

## Pattern: Tree Depth First Search

- [ ] <https://leetcode.com/problems/path-sum/>
- [ ] <https://leetcode.com/problems/path-sum-ii/>
- [ ] <https://leetcode.com/problems/sum-root-to-leaf-numbers/>
- [ ] <https://leetcode.com/problems/check-if-a-string-is-a-valid-sequence-from-root-to-leaves-path-in-a-binary-tree/description/>
- [ ] <https://leetcode.com/problems/path-sum-iii/>
- [ ] <https://leetcode.com/problems/diameter-of-binary-tree/>
- [ ] <https://leetcode.com/problems/binary-tree-maximum-path-sum/>

## Pattern: Two Heaps

- [ ] <https://leetcode.com/problems/find-median-from-data-stream/>
- [ ] <https://leetcode.com/problems/sliding-window-median/>
- [ ] <https://leetcode.com/problems/ipo/>
- [ ] <https://leetcode.com/problems/find-right-interval/>

## Pattern: Subsets

- [ ] <https://leetcode.com/problems/subsets/>
- [ ] <https://leetcode.com/problems/subsets-ii/>
- [ ] <https://leetcode.com/problems/permutations/>
- [ ] <https://leetcode.com/problems/letter-case-permutation/>
- [ ] <https://leetcode.com/problems/generate-parentheses/>
- [ ] <https://leetcode.com/problems/generalized-abbreviation/>
- [ ] <https://leetcode.com/problems/different-ways-to-add-parentheses/>
- [ ] <https://leetcode.com/problems/unique-binary-search-trees-ii/>
- [ ] <https://leetcode.com/problems/unique-binary-search-trees/>

## Pattern: Modified Binary Search

- [ ] <https://leetcode.com/problems/binary-search/>  # Close enough. The grokking problem allows sorted input arrays as ascending or descending, which only introduces a simple check
- [ ] Did not find. Problem is find index of smallest element greater or equal to input value
- [ ] <https://leetcode.com/problems/find-smallest-letter-greater-than-target/>
- [ ] <https://leetcode.com/problems/find-first-and-last-position-of-element-in-sorted-array/>
- [ ] <https://leetcode.com/problems/search-in-a-sorted-array-of-unknown-size/>
- [ ] <https://leetcode.com/problems/find-k-closest-elements/> (with K == 1)
- [ ] <https://leetcode.com/problems/peak-index-in-a-mountain-array/>
- [ ] <https://leetcode.com/problems/find-in-mountain-array/>
- [ ] <https://leetcode.com/problems/search-in-rotated-sorted-array/>
- [ ] Similar to previous, but find the number of rotations of the array.

## Pattern: Bitwise XOR

- [ ] <https://leetcode.com/problems/single-number/>
- [ ] <https://leetcode.com/problems/single-number-iii/>
- [ ] <https://leetcode.com/problems/complement-of-base-10-integer/>
- [ ] <https://leetcode.com/problems/flipping-an-image/>

## Pattern: Top 'K' elements

- [ ] Same as second question, but the first Grokking question wants the top K instead of the bottom K
- [ ] <https://leetcode.com/problems/kth-largest-element-in-an-array>
- [ ] <https://leetcode.com/problems/k-closest-points-to-origin/>
- [ ] <https://leetcode.com/problems/minimum-cost-to-connect-sticks/>
- [ ] <https://leetcode.com/problems/top-k-frequent-elements/>
- [ ] <https://leetcode.com/problems/sort-characters-by-frequency/>
- [ ] <https://leetcode.com/problems/kth-largest-element-in-a-stream/>
- [ ] <https://leetcode.com/problems/find-k-closest-elements/>
- [ ] <https://leetcode.com/problems/least-number-of-unique-integers-after-k-removals/> closest leetcode or <https://www.geeksforgeeks.org/maximum-distinct-elements-removing-k-elements/> for exact
- [ ] <https://www.geeksforgeeks.org/sum-elements-k1th-k2th-smallest-elements/> no leetcode equivalent found
- [ ] <https://leetcode.com/problems/reorganize-string/>
- [ ] <https://leetcode.com/problems/rearrange-string-k-distance-apart/>
- [ ] <https://leetcode.com/problems/task-scheduler/>
- [ ] <https://leetcode.com/problems/maximum-frequency-stack/>

## Pattern: K-way merge

- [ ] <https://leetcode.com/problems/merge-k-sorted-lists/>
- [ ] Same as previous, but return the Kth smallest number
- [ ] <https://leetcode.com/problems/kth-smallest-element-in-a-sorted-matrix/>
- [ ] <https://leetcode.com/problems/smallest-range-covering-elements-from-k-lists/>
- [ ] <https://leetcode.com/problems/find-k-pairs-with-smallest-sums/> small difference, grokking has different sort order and wants the largest

## Pattern: 0/1 Knapsack

- [ ] <https://www.educative.io/courses/grokking-dynamic-programming-patterns-for-coding-interviews/RM1BDv71V60>
- [ ] <https://www.educative.io/courses/grokking-dynamic-programming-patterns-for-coding-interviews/3jEPRo5PDvx> or <https://leetcode.com/problems/partition-equal-subset-sum/>
- [ ] <https://www.educative.io/courses/grokking-dynamic-programming-patterns-for-coding-interviews/3j64vRY6JnR>
- [ ] <https://leetcode.com/problems/last-stone-weight-ii/> similar concept, but problem description is more abstract.
- [ ] <https://leetcode.com/problems/combination-sum-ii/> similar, but return the number of combinations instead of the combinations
- [ ] <https://leetcode.com/problems/target-sum/>
- [ ] BONUS : Not in grokking, but I still found this very useful <https://leetcode.com/problems/ones-and-zeroes/>

## Pattern: Topological Sort

- First problem is identical to the following three
- [ ] <https://leetcode.com/problems/course-schedule/>
- [ ] <https://leetcode.com/problems/course-schedule-ii/>
  Same as above, but return all instead of any
- [ ] <https://leetcode.com/problems/alien-dictionary/>
- [ ] <https://leetcode.com/problems/sequence-reconstruction/description/>
- [ ] <https://leetcode.com/problems/minimum-height-trees/>

## Misc

- [ ] <https://leetcode.com/problems/kth-largest-element-in-an-array/>