# 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. ## 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/