30DaysCoding.com 150 Questions: Data structures Solve and understand these questions, make notes, watch solutions, and have fun. Don’t just solve them to get a job, but to learn something new! These are mostly internship-level questions (easy-medium), but will help you in general with problem solving! Arrays Easy - h ps://leetcode.com/problems/roman-to-integer/ - h ps://leetcode.com/problems/valid-parentheses/ - h ps://leetcode.com/problems/remove-duplicates-from-so ed-array/ - h ps://leetcode.com/problems/remove-element/ - h ps://leetcode.com/problems/best-time-to-buy-and-sell-stock/ - h ps://leetcode.com/problems/best-time-to-buy-and-sell-stock-ii/ - h ps://leetcode.com/problems/intersection-of-two-arrays-ii/ - h ps://leetcode.com/problems/single-number/ - h ps://leetcode.com/problems/contains-duplicate/ - h ps://leetcode.com/problems/plus-one/ - h ps://leetcode.com/problems/move-zeroes/ - h ps://leetcode.com/problems/rotate-image/ Medium - h ps://leetcode.com/problems/3sum/ - h ps://leetcode.com/problems/4sum/ - h ps://leetcode.com/problems/ nd- rst-and-last-position-of-element-in-so ed-array / - h ps://leetcode.com/problems/group-anagrams/ - h ps://leetcode.com/problems/reduce-array-size-to-the-half/ - h ps://leetcode.com/problems/merge-intervals/ 30DaysCoding.com Linked list Easy - h ps://leetcode.com/problems/delete-node-in-a-linked-list/ - h ps://leetcode.com/problems/remove-nth-node-from-end-of-list/ - h ps://leetcode.com/problems/merge-two-so ed-lists/ - h ps://leetcode.com/problems/palindrome-linked-list/ - h ps://leetcode.com/problems/linked-list-cycle/ Medium - h ps://leetcode.com/problems/intersection-of-two-linked-lists/ - h ps://leetcode.com/problems/remove-linked-list-elements/ - h ps://leetcode.com/problems/middle-of-the-linked-list/ - h ps://leetcode.com/problems/merge-k-so ed-lists/ Binary search Easy - h ps://leetcode.com/problems/binary-search/ - h ps://leetcode.com/problems/intersection-of-two-arrays/ - h ps://leetcode.com/problems/ rst-bad-version/ - h ps://leetcode.com/problems/arranging-coins/ - h ps://leetcode.com/problems/search-inse -position/ Medium - h ps://leetcode.com/problems/search-in-rotated-so ed-array/ - h ps://leetcode.com/problems/ nd- rst-and-last-position-of-element-in-so ed-array / - h ps://leetcode.com/problems/kth-smallest-element-in-a-bst/ - h ps://leetcode.com/problems/ nd-peak-element/ - h ps://leetcode.com/problems/split-array-largest-sum/ 30DaysCoding.com Sliding window Read - Leetcode Pa ern 2 | Sliding Windows for Strings | by csgator | Leetcode Pa erns Easy/Medium - h ps://leetcode.com/problems/longest-substring-without-repeating-characters/ - h ps://leetcode.com/problems/ nd-all-anagrams-in-a-string/description/ - h ps://leetcode.com/problems/minimum-window-substring/description/ - h ps://leetcode.com/problems/count-number-of-nice-subarrays/ - h ps://leetcode.com/problems/fruit-into-baskets/ 2 pointers - h ps://leetcode.com/problems/intersection-of-two-arrays/ - h ps://leetcode.com/problems/maximum-ascending-subarray-sum/ - h ps://leetcode.com/problems/backspace-string-compare/ - h ps://leetcode.com/problems/long-pressed-name/ - h ps://leetcode.com/problems/fruit-into-baskets/ - h ps://leetcode.com/problems/max-consecutive-ones-iii/ - h ps://leetcode.com/problems/container-with-most-water/ Stacks, Queues - Easy - h ps://leetcode.com/problems/valid-parentheses/ - h ps://leetcode.com/problems/implement-queue-using-stacks/ - h ps://leetcode.com/problems/min-stack/ - Medium - h ps://leetcode.com/problems/design-circular-queue/ - h ps://leetcode.com/problems/decode-string/ 30DaysCoding.com - h ps://leetcode.com/problems/open-the-lock/ - h ps://leetcode.com/problems/daily-temperatures/ - h ps://leetcode.com/problems/minimum-add-to-make-parentheses-valid/ BFS, DFS Read - Leetcode Pa ern 1 | BFS + DFS == 25% of the problems — pa 1 - Leetcode Pa ern 1 | DFS + BFS == 25% of the problems — pa 2 Questions - h ps://leetcode.com/problems/ ood- ll/ - h ps://leetcode.com/problems/binary-tree-preorder-traversal/ - h ps://leetcode.com/problems/number-of-islands/ - h ps://leetcode.com/problems/walls-and-gates/ - h ps://leetcode.com/problems/max-area-of-island/ - h ps://leetcode.com/problems/number-of-provinces/ - h ps://leetcode.com/problems/pe ect-squares/ - h ps://leetcode.com/problems/course-schedule/ - h ps://www.geeksforgeeks.org/detect-cycle-undirected-graph/ - h ps://leetcode.com/problems/word-ladder/ - h ps://leetcode.com/problems/01-matrix/ - h ps://leetcode.com/problems/ro ing-oranges/ - h ps://leetcode.com/problems/pe ect-squares/ - h ps://leetcode.com/problems/all-paths-from-source-to-target/ - h ps://leetcode.com/problems/number-of-closed-islands/ Recursion Easy - 509. Fibonacci Number - Reverse String 30DaysCoding.com - 24. Swap Nodes in Pairs - 206. Reverse Linked List - Leetcode #700 Search in a Binary Search Tree - 70. Climbing Stairs - Leetcode #50 Pow(x, n) Backtracking Read - Leetcode Pa ern 3 | Backtracking | by csgator | Leetcode Pa erns - A general approach to backtracking questions in Java (Subsets, Permutations, Combination Sum, Palindrome Pa itioning) Easy - Word Search - Leetcode #78 Subsets - 90. Subsets II - Le er Case Permutation Medium - 39. Combination Sum - 17. Le er Combinations of a Phone Number - Combinations - Leetcode : Combination Sum II - 216. Combination Sum III - Combination Sum IV - 46. Permutations - 47. Permutations II - 31. Next Permutation - 51. N-Queens 30DaysCoding.com Trees Read - Leetcode Pa ern 0 | Iterative traversals on Trees | by csgator | Leetcode Pa erns Easy - h ps://leetcode.com/problems/binary-tree-preorder-traversal/ - h ps://leetcode.com/problems/binary-tree-inorder-traversal/ - h ps://leetcode.com/problems/binary-tree-postorder-traversal/ - h ps://leetcode.com/problems/validate-binary-search-tree/ - h ps://leetcode.com/problems/minimum-distance-between-bst-nodes/ - h ps://leetcode.com/problems/symmetric-tree/ - h ps://leetcode.com/problems/same-tree/ - h ps://leetcode.com/problems/path-sum/ - h ps://leetcode.com/problems/maximum-depth-of-binary-tree/ - h ps://leetcode.com/problems/conve -so ed-array-to-binary-search-tree/ - Medium - h ps://leetcode.com/problems/validate-binary-search-tree/ - h ps://leetcode.com/problems/binary-search-tree-iterator/ - h ps://leetcode.com/problems/unique-binary-search-trees/ - h ps://leetcode.com/problems/serialize-and-deserialize-bst/ - h ps://leetcode.com/problems/binary-tree-right-side-view/ - h ps://leetcode.com/problems/binary-tree-level-order-traversal/ - h ps://leetcode.com/problems/binary-tree-level-order-traversal-ii/ - h ps://leetcode.com/problems/binary-tree-zigzag-level-order-traversal/ Dynamic programming Easy - h ps://leetcode.com/problems/maximum-subarray/ 30DaysCoding.com - h ps://leetcode.com/problems/ bonacci-number/ - h ps://leetcode.com/problems/climbing-stairs/ - h ps://leetcode.com/problems/min-cost-climbing-stairs/ - h ps://leetcode.com/problems/n-th-tribonacci-number/ Medium - h ps://leetcode.com/problems/coin-change/ - h ps://leetcode.com/problems/minimum-falling-path-sum/ - h ps://leetcode.com/problems/minimum-cost-for-tickets/ - h ps://leetcode.com/problems/2-keys-keyboard/ - h ps://leetcode.com/problems/maximum-product-subarray/ - h ps://leetcode.com/problems/triangle/ - h ps://leetcode.com/problems/ones-and-zeroes/ - h ps://leetcode.com/problems/longest-arithmetic-subsequence/ - h ps://leetcode.com/problems/pa ition-equal-subset-sum/ - h ps://leetcode.com/problems/house-robber/ - h ps://leetcode.com/problems/decode-ways/ - h ps://leetcode.com/problems/word-break/ - h ps://leetcode.com/problems/edit-distance/ - h ps://leetcode.com/problems/longest-increasing-subsequence/ Graphs Easy - h ps://leetcode.com/problems/employee-impo ance/ - h ps://leetcode.com/problems/ nd-the-town-judge/ Medium - h ps://leetcode.com/problems/course-schedule-ii/ - h ps://leetcode.com/problems/redundant-connection/ - h ps://leetcode.com/problems/surrounded-regions/ - h ps://leetcode.com/problems/accounts-merge/ 30DaysCoding.com - h ps://leetcode.com/problems/network-delay-time/ - h ps://leetcode.com/problems/is-graph-bipa ite/ - h ps://leetcode.com/problems/ nd-eventual-safe-states/ - h ps://leetcode.com/problems/keys-and-rooms/ - h ps://leetcode.com/problems/possible-bipa ition/ - h ps://leetcode.com/problems/most-stones-removed-with-same-row-or-column/ - h ps://leetcode.com/problems/ro ing-oranges/ - h ps://leetcode.com/problems/number-of-operations-to-make-network-connected/ Additional questions - h ps://leetcode.com/problems/longest-common-pre x/ - h ps://leetcode.com/problems/implement-trie-pre x-tree/ Random - h ps://leetcode.com/explore/ Videos Some long videos, to revise or study in one long stretch! - Data Structures Easy to Advanced Course - Full Tutorial from a Google Engineer - Introduction to Data Structures & Algorithms | Course Details & Prerequisites - Algorithms Course - Graph Theory Tutorial from a Google Engineer