## Core Pillars ### Patterns - Two Pointers: - Fast and Slow Pointers: 1 - Sliding Window: 15 - Merge Intervals: 7 - Cyclic Sort: 3 - Linked List Reversal: 4 - Stack: - Monotonic Stack: 5 - Hash Map: 38 - Tree Traversals: - Level Order Traversal: 12 - Tree Breadth First Search: 4 - Tree Depth First Search: 6 - Graph: 24 - Matrix Traversal: 1 - Subsets: 8 - Bitwise XOR: 1 - Top K Elements: 7 - K-way Merge: 5 - Greedy Algorithm: 39 - 0/1 Knapsack: 1 - Backtracking: 33 - Trie: 5 - Topological Sort: 7 - Union-Find: 3 - Prefix Sum: 8 - Counting: 24 - Simulation: 5 - Linear Sorting: 1 - Serialize and Deserialize: 1 - Clone: 1 ## Difficulty | # | Title | Acceptance | Difficulty | |----|-----------------------------------------------------------------------------------------|------------|------------| | 1 | [Contains Duplicate (easy)](/content/problem/coding/contains-duplicate-easy/index.html) | 55.5% | easy | | 2 | [Pangram (easy)](/content/problem/coding/pangram-easy/index.html) | 31.1% | easy | | 3 | [Reverse Vowels (easy)](/content/problem/coding/reverse-vowels-easy/index.html) | 44.3% | easy | | 4 | [Valid Palindrome (easy)](/content/problem/coding/valid-palindrome-easy/index.html) | 22.6% | easy | | 5 | [Valid Anagram (easy)](/content/problem/coding/valid-anagram-easy/index.html) | 38.4% | easy | | 6 | [Shortest Word Distance (easy)](/content/problem/coding/shortest-word-distance-easy/index.html) | 27.9% | easy | | 7 | [Number of Good Pairs (easy)](/content/problem/coding/number-of-good-pairs-easy/index.html) | 75.4% | easy | | 8 | [Sqrt (medium)](/content/problem/coding/sqrt-medium/index.html) | 15.4% | Med. | | 9 | [Pair with Target Sum (easy)](/content/problem/coding/pair-with-target-sum-easy/index.html) | 42.4% | easy | | 10 | [Find Non-Duplicate Number Instances (easy)](/content/problem/coding/find-nonduplicate-number-instances-easy/index.html) | 42.5% | easy | | 11 | [Squaring a Sorted Array (easy)](/content/problem/coding/squaring-a-sorted-array-easy/index.html) | 35.6% | easy | | 12 | [Triplet Sum to Zero (medium)](/content/problem/coding/triplet-sum-to-zero-medium/index.html) | 22.2% | Med. | | 13 | [Triplet Sum Close to Target (medium)](/content/problem/coding/triplet-sum-close-to-target-medium/index.html) | 12.2% | Med. | | 14 | [Triplets with Smaller Sum (medium)](/content/problem/coding/triplets-with-smaller-sum-medium/index.html) | 22.7% | Med. | | 15 | [Dutch National Flag Problem (medium)](/content/problem/coding/dutch-national-flag-problem-medium/index.html) | 29.6% | Med. | | 16 | [Problem Challenge 1: Quadruple Sum to Target (medium)](/content/problem/coding/problem-challenge-1-quadruple-sum-to-target-medium/index.html) | 17.3% | Med. | | 17 | [Problem Challenge 2: Comparing Strings containing Backspaces (medium)](/content/problem/coding/problem-challenge-2-comparing-strings-containing-backspaces-medium/index.html) | 16.8% | Med. | | 18 | [Problem Challenge 3: Minimum Window Sort (medium)](/content/problem/coding/problem-challenge-3-minimum-window-sort-medium/index.html) | 12.7% | Med. | | 19 | [LinkedList Cycle (easy)](/content/problem/coding/linkedlist-cycle-easy/index.html) | 64.5% | easy | | 20 | [Middle of the LinkedList (easy)](/content/problem/coding/middle-of-the-linkedlist-easy/index.html) | 59.9% | easy | | 21 | [Start of LinkedList Cycle (medium)](/content/problem/coding/start-of-linkedlist-cycle-medium/index.html) | 49.7% | Med. | | 22 | [Happy Number (medium)](/content/problem/coding/happy-number-medium/index.html) | 47.2% | Med. | | 23 | [Problem Challenge 1: Palindrome LinkedList (medium)](/content/problem/coding/problem-challenge-1-palindrome-linkedlist-medium/index.html) | 28.9% | Med. | | 24 | [Problem Challenge 2: Rearrange a LinkedList (medium)](/content/problem/coding/problem-challenge-2-rearrange-a-linkedlist-medium/index.html) | 56.3% | Med. | | 25 | [Problem Challenge 3: Cycle in a Circular Array (hard)](/content/problem/coding/problem-challenge-3-cycle-in-a-circular-array-hard/index.html) | 17.2% | hard | | 26 | [Maximum Sum Subarray of Size K (easy)](/content/problem/coding/maximum-sum-subarray-of-size-k-easy/index.html) | 46.3% | easy | | 27 | [Smallest Subarray With a Greater Sum (easy)](/content/problem/coding/smallest-subarray-with-a-greater-sum-easy/index.html) | 19.7% | easy | | 28 | [Longest Substring with K Distinct Characters (medium)](/content/problem/coding/longest-substring-with-k-distinct-characters-medium/index.html) | 28.0% | Med. | | 29 | [Fruits into Baskets (medium)](/content/problem/coding/fruits-into-baskets-medium/index.html) | 39.5% | Med. | | 30 | [Longest Substring with Same Letters after Replacement (hard)](/content/problem/coding/longest-substring-with-same-letters-after-replacement-hard/index.html) | 29.9% | hard | | 31 | [Longest Subarray with Ones after Replacement (hard)](/content/problem/coding/longest-subarray-with-ones-after-replacement-hard/index.html) | 48.7% | hard | | 32 | [Problem Challenge 1: Permutation in a String (hard)](/content/problem/coding/problem-challenge-1-permutation-in-a-string-hard/index.html) | 16.3% | hard | | 33 | [Problem Challenge 2: String Anagrams (hard)](/content/problem/coding/problem-challenge-2string-anagrams-hard/index.html) | 29.1% | hard | | 34 | [Problem Challenge 3: Smallest Window containing Substring (hard)](/content/problem/coding/problem-challenge-3-smallest-window-containing-substring-hard/index.html) | 20.0% | hard | | 35 | [Problem Challenge 4: Words Concatenation (hard)](/content/problem/coding/problem-challenge-4-words-concatenation-hard/index.html) | 23.2% | hard | | 36 | [Problem Challenge 5: Counting Subarrays with Product Less than a Target (hard)](/content/problem/coding/problem-challenge-5-counting-subarrays-with-product-less-than-a-target-medium/index.html) | 29.0% | hard | | 37 | [Problem Challenge 6: Subarrays with Product Less than a Target (hard)](/content/problem/coding/problem-challenge-6-subarrays-with-product-less-than-a-target-medium/index.html) | 24.8% | hard | | 38 | [Merge Intervals (medium)](/content/problem/coding/merge-intervals-medium/index.html) | 31.3% | Med. | | 39 | [Insert Interval (medium)](/content/problem/coding/insert-interval-medium/index.html) | 22.0% | Med. | | 40 | [Intervals Intersection (medium)](/content/problem/coding/intervals-intersection-medium/index.html) | 48.0% | Med. | | 41 | [Conflicting Appointments (medium)](/content/problem/coding/conflicting-appointments-medium/index.html) | 28.1% | Med. | | 42 | [Problem Challenge 1: Minimum Meeting Rooms (hard)](/content/problem/coding/problem-challenge-1-minimum-meeting-rooms-hard/index.html) | 25.8% | hard | | 43 | [Problem Challenge 2: Maximum CPU Load (hard)](/content/problem/coding/problem-challenge-2-maximum-cpu-load-hard/index.html) | 43.1% | hard | | 44 | [Problem Challenge 3: Employee Free Time (hard)](/content/problem/coding/problem-challenge-3-employee-free-time-hard/index.html) | 48.4% | hard | | 45 | [Cyclic Sort (easy)](/content/problem/coding/cyclic-sort-easy/index.html) | 48.3% | easy | | 46 | [Find the Missing Number (easy)](/content/problem/coding/find-the-missing-number-easy/index.html) | 42.5% | easy | | 47 | [Find all Missing Numbers (easy)](/content/problem/coding/find-all-missing-numbers-easy/index.html) | 54.3% | easy | | 48 | [Find the Duplicate Number (easy)](/content/problem/coding/find-the-duplicate-number-easy/index.html) | 49.1% | easy | | 49 | [Find all Duplicate Numbers (easy)](/content/problem/coding/find-all-duplicate-numbers-easy/index.html) | 67.2% | easy | | 50 | [Problem Challenge 1: Find the Corrupt Pair (easy)](/content/problem/coding/problem-challenge-1-find-the-corrupt-pair-easy/index.html) | 48.1% | easy | | 51 | [Problem Challenge 2: Find the Smallest Missing Positive Number (medium)](/content/problem/coding/problem-challenge-2-find-the-smallest-missing-positive-number-medium/index.html) | 28.9% | Med. | | 52 | [Problem Challenge 3: Find the First K Missing Positive Numbers (hard)](/content/problem/coding/problem-challenge-3-find-the-first-k-missing-positive-numbers-hard/index.html) | 16.7% | hard | | 53 | [Reverse a LinkedList (easy)](/content/problem/coding/reverse-a-linkedlist-easy/index.html) | 80.1% | easy | | 54 | [Reverse a Sub-list (medium)](/content/problem/coding/reverse-a-sublist-medium/index.html) | 31.4% | Med. | | 55 | [Reverse every K-element Sub-list (medium)](/content/problem/coding/reverse-every-kelement-sublist-medium/index.html) | 53.1% | Med. | | 56 | [Problem Challenge 1: Reverse alternating K-element Sub-list (medium)](/content/problem/coding/problem-challenge-1-reverse-alternating-kelement-sublist-medium/index.html) | 51.7% | Med. | | 57 | [Problem Challenge 2: Rotate a LinkedList (medium)](/content/problem/coding/problem-challenge-2-rotate-a-linkedlist-medium/index.html) | 22.9% | Med. | | 58 | [Problem 1: Balanced Parentheses (easy)](/content/problem/coding/problem-1-balanced-parentheses/index.html) | 30.1% | easy | | 59 | [Problem 2: Reverse a String (easy)](/content/problem/coding/problem-2-reverse-a-string/index.html) | 85.1% | easy | | 60 | [Problem 3: Decimal to Binary Conversion (medium)](/content/problem/coding/problem-3-decimal-to-binary-conversion/index.html) | 46.7% | Med. | | 61 | [Problem 4: Next Greater Element (easy)](/content/problem/coding/problem-4-next-greater-element/index.html) | 31.5% | easy | | 62 | [Problem 5: Sorting a Stack (easy)](/content/problem/coding/problem-5-sorting-a-stack/index.html) | 69.7% | easy | | 63 | [Problem 6: Simplify Path (medium)](/content/problem/coding/problem-6-simplify-path/index.html) | 25.2% | Med. | | 64 | [Remove Nodes From Linked List (easy)](/content/problem/coding/remove-nodes-from-linked-list-easy/index.html) | 41.9% | easy | | 65 | [Remove All Adjacent Duplicates In String (easy)](/content/problem/coding/remove-all-adjacent-duplicates-in-string-easy/index.html) | 58.6% | easy | | 66 | [Next Greater Element (easy)](/content/problem/coding/next-greater-element-easy/index.html) | 55.4% | easy | | 67 | [Daily Temperatures (easy)](/content/problem/coding/daily-temperatures-easy/index.html) | 54.9% | easy | | 68 | [Remove All Adjacent Duplicates in String II (medium)](/content/problem/coding/remove-all-adjacent-duplicates-in-string-ii-medium/index.html) | 37.1% | Med. | | 69 | [Sum of Subarray Minimums (medium)](/content/problem/coding/sum-of-subarray-minimums-medium-1/index.html) | 67.6% | Med. | | 70 | [Remove K Digits (hard)](/content/problem/coding/remove-k-digits-hard/index.html) | 12.6% | hard | | 71 | [Problem 1: First Non-repeating Character (easy)](/content/problem/coding/problem-1-first-nonrepeating-character-easy/index.html) | 55.3% | easy | | 72 | [Solution: First Non-repeating Character (easy)](/content/problem/coding/solution-first-nonrepeating-character-easy/index.html) | 0.0% | easy | | 73 | [Problem 2: Largest Unique Number (easy)](/content/problem/coding/problem-2-largest-unique-number-easy/index.html) | 61.4% | easy | | 74 | [Solution: Largest Unique Number (easy)](/content/problem/coding/solution-largest-unique-number-easy/index.html) | 0.0% | easy | | 75 | [Problem 3: Maximum Number of Balloons (easy)](/content/problem/coding/problem-3-maximum-number-of-balloons-easy/index.html) | 39.7% | easy | | 76 | [Solution: Maximum Number of Balloons (easy)](/content/problem/coding/solution-maximum-number-of-balloons-easy/index.html) | 0.0% | easy | | 77 | [Problem 4: Longest Palindrome (easy)](/content/problem/coding/problem-4-longest-palindromeeasy/index.html) | 24.1% | easy | | 78 | [Solution: Longest Palindrome (easy)](/content/problem/coding/solution-longest-palindromeeasy/index.html) | 0.0% | easy | | 79 | [Problem 5: Ransom Note (easy)](/content/problem/coding/problem-5-ransom-note-easy/index.html) | 56.7% | easy | | 80 | [Solution: Ransom Note (easy)](/content/problem/coding/solution-ransom-note-easy/index.html) | 0.0% | easy | | 81 | [Binary Tree Level Order Traversal (easy)](/content/problem/coding/binary-tree-level-order-traversal-easy/index.html) | 73.5% | easy | | 82 | [Reverse Level Order Traversal (easy)](/content/problem/coding/reverse-level-order-traversal-easy/index.html) | 89.2% | easy | | 83 | [Zigzag Traversal (medium)](/content/problem/coding/zigzag-traversal-medium/index.html) | 64.1% | Med. | | 84 | [Level Averages in a Binary Tree (easy)](/content/problem/coding/level-averages-in-a-binary-tree-easy/index.html) | 82.0% | easy | | 85 | [Find Largest Value in Each Tree Row (medium)](/content/problem/coding/find-largest-value-in-each-tree-row-medium/index.html) | 90.5% | Med. | | 86 | [Maximum Level Sum of a Binary Tree (medium)](/content/problem/coding/maximum-level-sum-of-a-binary-tree-medium/index.html) | 54.0% | Med. | | 87 | [Even Odd Tree (medium)](/content/problem/coding/even-odd-tree-medium/index.html) | 56.9% | Med. | | 88 | [Minimum Depth of a Binary Tree (easy)](/content/problem/coding/minimum-depth-of-a-binary-tree-easy/index.html) | 21.5% | easy | | 89 | [Level Order Successor (easy)](/content/problem/coding/level-order-successor-easy/index.html) | 63.9% | easy | | 90 | [Connect Level Order Siblings (medium)](/content/problem/coding/connect-level-order-siblings-medium/index.html) | 78.1% | Med. | | 91 | [Maximum Width of Binary Tree (medium)](/content/problem/coding/maximum-width-of-binary-tree-medium/index.html) | 32.1% | Med. | | 92 | [N-ary Tree Level Order Traversal (hard)](/content/problem/coding/nary-tree-level-order-traversal-hard/index.html) | 92.5% | hard | | 93 | [Problem Challenge 1: Connect All Level Order Siblings (medium)](/content/problem/coding/problem-challenge-1-connect-all-level-order-siblings-medium/index.html) | 80.1% | Med. | | 94 | [Problem Challenge 2: Right View of a Binary Tree (easy)](/content/problem/coding/problem-challenge-2-right-view-of-a-binary-tree-easy/index.html) | 76.3% | easy | | 95 | [Binary Tree Path Sum (easy)](/content/problem/coding/binary-tree-path-sum-easy/index.html) | 38.3% | easy | | 96 | [All Paths for a Sum (medium)](/content/problem/coding/all-paths-for-a-sum-medium/index.html) | 56.9% | Med. | | 97 | [Sum of Path Numbers (medium)](/content/problem/coding/sum-of-path-numbers-medium/index.html) | 69.0% | Med. | | 98 | [Path With Given Sequence (medium)](/content/problem/coding/path-with-given-sequence-medium/index.html) | 25.9% | Med. | | 99 | [Count Paths for a Sum (medium)](/content/problem/coding/count-paths-for-a-sum-medium/index.html) | 24.5% | Med. | | 100 | [Problem Challenge 1: Tree Diameter (medium)](/content/problem/coding/problem-challenge-1-tree-diameter-medium/index.html) | 59.3% | Med. |