# Common Data Structures and Algorithms Patterns ## Pattern 1: Fast and Slow Pointers | **Problem Link** | **Articles** | **Solution** | | --- | --- | --- | | [Linked List Cycle](https://leetcode.com/problems/linked-list-cycle/description/) | | [Github](https://github.com/subhakundu/DsAlgoPractice/blob/main/FastAndSlowPointers/LinkedListCycle/Solution.java) | | [Happy Number](https://leetcode.com/problems/happy-number/description/) | | [Github](https://github.com/subhakundu/DsAlgoPractice/blob/main/FastAndSlowPointers/HappyNumber/Solution.java) | | [Find the duplicate number](https://leetcode.com/problems/find-the-duplicate-number/description/) | | | ## Pattern 2: Sliding Window | **Problem Link** | **Articles** | **Solution** | | --- | --- | --- | | [Maximum Average Subarray](https://leetcode.com/problems/maximum-average-subarray-i/description/) | | [Github](https://github.com/subhakundu/DsAlgoPractice/blob/main/SlidingWindow/MaximumAverageSubarray/Solution.java) | | [Longest Substring Without Repeating Character](https://leetcode.com/problems/longest-substring-without-repeating-characters/description/) | | [Github](https://github.com/subhakundu/DsAlgoPractice/blob/main/SlidingWindow/LongestSubstringWithoutRepeatingCharacters/Solution.java) | | [Minimum window substring](https://leetcode.com/problems/minimum-window-substring/description/) | | [Github](https://github.com/subhakundu/DsAlgoPractice/blob/main/SlidingWindow/MinimumWindowSubstring/Solution.java) | ## Pattern 3: Merge Intervals/Overlapping Intervals | **Problem Link** | **Articles** | **Solution** | | --- | --- | --- | | [Merge Intervals](https://leetcode.com/problems/merge-intervals/description/) | | [Github](https://github.com/subhakundu/DsAlgoPractice/blob/main/MergedIntervals/MergeIntervals/Solution.java) | | [Insert Intervals](https://leetcode.com/problems/insert-interval/description/) | | [Linear Search](https://github.com/subhakundu/DsAlgoPractice/blob/main/MergedIntervals/InsertIntervals/LinearSearch/Solution.java), [Binary Search](https://github.com/subhakundu/DsAlgoPractice/blob/main/MergedIntervals/InsertIntervals/BinarySearch/Solution.java) | | [Non-overlapping Intervals](https://leetcode.com/problems/non-overlapping-intervals/description/) | | | ## Pattern 4: **LinkedList In-place Reversal** | **Problem Link** | **Articles** | **Solution** | | --- | --- | --- | | [Reverse Linked List](https://leetcode.com/problems/reverse-linked-list/description/) | | [Iterative](https://github.com/subhakundu/DsAlgoPractice/blob/main/LinkedListInPlaceReversal/Iterative/Solution.java), [Recursive](https://github.com/subhakundu/DsAlgoPractice/blob/main/LinkedListInPlaceReversal/Recursive/Solution.java) | | [Reverse Linked List II](https://leetcode.com/problems/reverse-linked-list-ii/description/) | | | | [Swap Nodes in Pairs](https://leetcode.com/problems/swap-nodes-in-pairs/description/) | | | ## Pattern 5: Prefix Sum | **Problem Link** | **Articles** | **Solution** | | --- | --- | --- | | [Range Sum Query - Immutable](https://leetcode.com/problems/range-sum-query-immutable/description/) | | [Github](https://github.com/subhakundu/DsAlgoPractice/blob/main/PrefixSum/RangeSumQuery.java) | | [Contiguous Array](https://leetcode.com/problems/contiguous-array/description/) | | [Github](https://github.com/subhakundu/DsAlgoPractice/blob/main/PrefixSum/ContiguousArray.java) | | [Subarray Sum Equals K](https://leetcode.com/problems/subarray-sum-equals-k/description/) | | [Github](https://github.com/subhakundu/DsAlgoPractice/tree/main/PrefixSum/SubarraySumEqualsK) | ## Pattern 6: **Top ‘K’ Elements** | **Problem Link** | **Articles** | **Solution** | | --- | --- | --- | | [Kth Largest Element in an Array](https://leetcode.com/problems/kth-largest-element-in-an-array/description/) | | [Github](https://github.com/subhakundu/DsAlgoPractice/blob/main/Heap/KthLargetElementInAnArray.java) | | [Top K Frequent Elements](https://leetcode.com/problems/top-k-frequent-elements/description/) | | [Github](https://github.com/subhakundu/DsAlgoPractice/blob/main/Heap/TopKFrequentElements.java) | | [Find K Pairs with Smallest Sums](https://leetcode.com/problems/find-k-pairs-with-smallest-sums/description/) | | [Github](https://github.com/subhakundu/DsAlgoPractice/blob/main/Heap/FindKPairsWithSmallestSum.java) | ## Pattern 7: Binary Search | **Problem Link** | **Articles** | **Solution** | | --- | --- | --- | | [Search in a rotated sorted array](https://leetcode.com/problems/search-in-rotated-sorted-array/description/) | | [Github](https://github.com/subhakundu/DsAlgoPractice/tree/main/BinarySearch/FindingElementInRotatedArray) | | [Find Minimum in a rotated sorted array](https://leetcode.com/problems/find-minimum-in-rotated-sorted-array/description/) | | [Github](https://github.com/subhakundu/DsAlgoPractice/blob/main/BinarySearch/FindMinimumInRotatedSortedArray.java) | | [Search a 2D matrix II](https://leetcode.com/problems/search-a-2d-matrix-ii/description/) | | [Github](https://github.com/subhakundu/DsAlgoPractice/tree/main/BinarySearch/SearchInA2DMatrix) | ## Pattern 8: Binary Tree Traversal | **Problem Link** | **Articles** | **Solution** | | --- | --- | --- | | [Binary Tree Paths](https://leetcode.com/problems/binary-tree-paths/description/) | | [Github](https://github.com/subhakundu/DsAlgoPractice/blob/main/BinaryTreeTraversal/BinaryTreePaths.java) | | [K-th Smallest Element in BST](https://leetcode.com/problems/kth-smallest-element-in-a-bst/description/) | | [Recursive](https://github.com/subhakundu/DsAlgoPractice/blob/main/BinaryTreeTraversal/KthSmallestElement/Recursive/Solution.java), [Iterative](https://github.com/subhakundu/DsAlgoPractice/blob/main/BinaryTreeTraversal/KthSmallestElement/Iterative/Solution.java) | | [Binary Tree Maximum Path Sum](https://leetcode.com/problems/binary-tree-maximum-path-sum/description/) | | | | [Inorder Traversal](https://leetcode.com/problems/binary-tree-inorder-traversal/description/) | | [Github](https://github.com/subhakundu/DsAlgoPractice/tree/main/Tree/InorderTraversal) | | [Symmetric Tree](https://leetcode.com/problems/symmetric-tree/description/) | | [Github](https://github.com/subhakundu/DsAlgoPractice/blob/main/Tree/SymmetricTree/Solution.java) | ## Pattern 9: Depth First Search | **Problem Link** | **Articles** | **Solution** | | --- | --- | --- | | [Clone Graph](https://leetcode.com/problems/clone-graph/description/) | | [Github](https://github.com/subhakundu/DsAlgoPractice/blob/main/Graph/ClonedGraph/DFS.java) | | [Path Sum II](https://leetcode.com/problems/path-sum-ii/description/) | | [Github](https://github.com/subhakundu/DsAlgoPractice/blob/main/Tree/PathSum2/Solution.java) | | [Course Schedule II](https://leetcode.com/problems/course-schedule-ii/description/) | | | | [Same Tree](https://leetcode.com/problems/same-tree/description/) | | [Github](https://github.com/subhakundu/DsAlgoPractice/blob/main/DepthFirstSearch/SameTree/Solution.java) | | [Number of Provinces](https://leetcode.com/problems/number-of-provinces/) | | [Github](https://github.com/subhakundu/DsAlgoPractice/blob/main/Graph/NumberOfProvinces/Solution.java) (DFS) | ## Pattern 10: Breadth First Search | **Problem Link** | **Articles** | **Solution** | | --- | --- | --- | | [Level Order Traversal](https://leetcode.com/problems/binary-tree-level-order-traversal/description/) | | [GitHub](https://github.com/subhakundu/DsAlgoPractice/blob/main/BreadthFirstSearch/BinaryTreeLevelOrderTraversal.java) | | [Rotting Oranges](https://leetcode.com/problems/rotting-oranges/description/) | | [Github](https://github.com/subhakundu/DsAlgoPractice/blob/main/Graph/RottenOranges/Solution.java) | | [Word Ladder](https://leetcode.com/problems/word-ladder/description/) | | | | [Clone Graph](https://leetcode.com/problems/clone-graph/description/) | | [Github](https://github.com/subhakundu/DsAlgoPractice/blob/main/Graph/ClonedGraph/BFS.java) | | [If Path Exists](https://leetcode.com/problems/find-if-path-exists-in-graph/description/) | | [BFS](https://github.com/subhakundu/DsAlgoPractice/blob/main/Graph/PathFinding/IfPathExists/BFS/Solution.java), [Union Find](https://github.com/subhakundu/DsAlgoPractice/blob/main/Graph/PathFinding/IfPathExists/UnionFind/Solution.java) | ## Pattern 11: **Matrix Traversal** | **Problem Link** | **Articles** | **Solution** | | --- | --- | --- | | [Flood Fill](https://leetcode.com/problems/flood-fill/description/) | | [Github](https://github.com/subhakundu/DsAlgoPractice/blob/main/Graph/Matrix/FloodFill/Solution.java) | | [Number of Islands](https://leetcode.com/problems/number-of-islands/description/) | | [Github](https://github.com/subhakundu/DsAlgoPractice/blob/main/Graph/Matrix/NumberOfIslands/Solution.java) | | [Surrounded Regions](https://leetcode.com/problems/surrounded-regions/description/) | | [Github](https://github.com/subhakundu/DsAlgoPractice/blob/main/Graph/Matrix/SurroundedRegions/Solution.java) | | [Number of Closed Islands](https://leetcode.com/problems/number-of-closed-islands/description/) | | [Without global variable](https://github.com/subhakundu/DsAlgoPractice/tree/main/Graph/Matrix/NumberOfClosedIslands/WithoutGlobalVariable), [with global variable](https://github.com/subhakundu/DsAlgoPractice/tree/main/Graph/Matrix/NumberOfClosedIslands/WithGlobalVariable) (cleaner, but not best practice) | ## Pattern 12: Backtracking | **Problem Link** | **Articles** | **Solution** | | --- | --- | --- | | [Permutations](https://leetcode.com/problems/permutations/description/) | [Notes](https://blog.thecuriouscoder.in/backtracking-generating-permutations) | [Github](https://github.com/subhakundu/DsAlgoPractice/blob/main/Backtracking/Permutations.java) | | [Subsets](https://leetcode.com/problems/subsets/description/) | | [Github](https://github.com/subhakundu/DsAlgoPractice/blob/main/Backtracking/Subsets.java) | | [N-queens](https://leetcode.com/problems/n-queens/description/) | | | ## Pattern 13: Monotonic Stack | **Problem Link** | **Articles** | **Solution** | | --- | --- | --- | | [Next Greater Element I](https://leetcode.com/problems/next-greater-element-i/description/) | | [Github](https://github.com/subhakundu/DsAlgoPractice/blob/main/MonotonicStack/NextGreaterElementI/Solution.java) | | [Daily Temperatures](https://leetcode.com/problems/daily-temperatures/description/) | | | | [Largest Rectangle in Histogram](https://leetcode.com/problems/largest-rectangle-in-histogram/description/) | | | ## Pattern 14: Generic Graphs | **Problem Link** | **Articles** | **Solution** | | --- | --- | --- | | [Minimum Number of Vertices to Reach All Nodes](https://leetcode.com/problems/minimum-number-of-vertices-to-reach-all-nodes/description/) | | [Solution](https://github.com/subhakundu/DsAlgoPractice/blob/main/Graph/MinimumNumberOfVertices/Solution.java) | | | | |