A pattern-first data structures and algorithms reference: 22 patterns, each with a copy-paste Java template, and worked walkthroughs for the Blind 75 and beyond.https://dsa-grind.pages.dev/enhttps://dsa-grind.pages.dev/maang-prep/overview/https://dsa-grind.pages.dev/maang-prep/overview/Target: SDE-II / L4 / E4 at Meta, Amazon, Apple, Netflix, Google (and Microsoft tier) Current profile: 3.5+ yrs, Jio Platform (ex-Karkinos Health)…Sun, 30 Aug 2026 07:17:55 GMTMAANG Interview Prepoverviewhttps://dsa-grind.pages.dev/start-here/overview/https://dsa-grind.pages.dev/start-here/overview/Knowing why you chose a Deque over a Stack or how HashMap resizing affects your O(n) time is what separates a Senior from a Junior candidate.Sun, 30 Aug 2026 07:17:11 GMTStart Hereoverviewhttps://dsa-grind.pages.dev/start-here/templates/https://dsa-grind.pages.dev/start-here/templates/One page. Every skeleton. Each pattern's full template section (with knobs, rules, and gotchas) lives in NN-Pattern/pattern-guide.md under ## 0. The…Sun, 30 Aug 2026 07:16:39 GMTStart Herenotehttps://dsa-grind.pages.dev/graph-patterns/pattern-guide/https://dsa-grind.pages.dev/graph-patterns/pattern-guide/Graphs have six algorithm templates (all spelled out in §3 below) but only one setup step — and that setup is where most interview time is actually lost…Sun, 30 Aug 2026 07:15:15 GMTGraph Patternsguidehttps://dsa-grind.pages.dev/tries/pattern-guide/https://dsa-grind.pages.dev/tries/pattern-guide/One node class, three methods. insert and search are the same 6-line walk; only the final check differs.Sun, 30 Aug 2026 07:14:34 GMTTriesguidehttps://dsa-grind.pages.dev/greedy/pattern-guide/https://dsa-grind.pages.dev/greedy/pattern-guide/Greedy is almost always sort by the right key, then one linear sweep. Choosing the sort key is the problem; the sweep is four lines.Sun, 30 Aug 2026 07:14:34 GMTGreedyguidehttps://dsa-grind.pages.dev/union-find/pattern-guide/https://dsa-grind.pages.dev/union-find/pattern-guide/One class. Memorise it verbatim — it's ~20 lines and it solves an entire category of graph problems that would otherwise need DFS plus bookkeeping.Sun, 30 Aug 2026 07:14:34 GMTUnion-Find (DSU)guidehttps://dsa-grind.pages.dev/top-k-elements/pattern-guide/https://dsa-grind.pages.dev/top-k-elements/pattern-guide/The counter-intuitive rule: for the k LARGEST, use a MIN-heap of size k. The top is the weakest survivor, so it is exactly the one to evict when something…Sun, 30 Aug 2026 07:14:34 GMTTop 'K' Elementsguidehttps://dsa-grind.pages.dev/dynamic-programming/pattern-guide/https://dsa-grind.pages.dev/dynamic-programming/pattern-guide/Two skeletons — top-down memo and bottom-up table. Write the recurrence first, in English, before you touch either.Sun, 30 Aug 2026 07:14:34 GMTDynamic Programmingguidehttps://dsa-grind.pages.dev/backtracking-subsets/pattern-guide/https://dsa-grind.pages.dev/backtracking-subsets/pattern-guide/Every backtracking problem is choose → explore → un-choose. The only thing that varies is the loop's start index and the pruning condition.Sun, 30 Aug 2026 07:14:34 GMTBacktracking & Subsetsguidehttps://dsa-grind.pages.dev/binary-search/pattern-guide/https://dsa-grind.pages.dev/binary-search/pattern-guide/Three skeletons. Template B (find the boundary) is the one to memorise — it solves far more interview problems than the exact-match version, and it never…Sun, 30 Aug 2026 07:14:34 GMTBinary Search (Modified)guidehttps://dsa-grind.pages.dev/bfs/pattern-guide/https://dsa-grind.pages.dev/bfs/pattern-guide/One skeleton, three surfaces: tree, grid, generic graph. The line that makes it work is int size = queue.size(); — freeze it, or your levels bleed into each…Sun, 30 Aug 2026 07:14:34 GMTBFSguidehttps://dsa-grind.pages.dev/dfs/pattern-guide/https://dsa-grind.pages.dev/dfs/pattern-guide/DFS is one recursive shape reused four ways. Pick your traversal order (when you touch the node) and whether you return a value up or carry state down.Sun, 30 Aug 2026 07:14:34 GMTDFSguidehttps://dsa-grind.pages.dev/two-heaps/pattern-guide/https://dsa-grind.pages.dev/two-heaps/pattern-guide/A max-heap of the smaller half and a min-heap of the larger half, kept balanced. The two heap tops straddle the median, so the median is O(1).Sun, 30 Aug 2026 07:14:34 GMTTwo Heapsguidehttps://dsa-grind.pages.dev/merge-intervals/pattern-guide/https://dsa-grind.pages.dev/merge-intervals/pattern-guide/Sort first, then a single linear sweep. Sort by start to merge; sort by end for greedy "max non-overlapping"; use a min-heap of end times for room/resource…Sun, 30 Aug 2026 07:14:34 GMTMerge Intervalsguidehttps://dsa-grind.pages.dev/cyclic-sort/pattern-guide/https://dsa-grind.pages.dev/cyclic-sort/pattern-guide/The trigger is narrow but unmistakable: n numbers drawn from the range 1..n (or 0..n-1), and the interviewer wants O(1) extra space. The array itself…Sun, 30 Aug 2026 07:14:34 GMTCyclic Sortguidehttps://dsa-grind.pages.dev/linked-list-reversal/pattern-guide/https://dsa-grind.pages.dev/linked-list-reversal/pattern-guide/Two skeletons — reverse and dummy head — plus one rule: when a problem might delete or replace the head, allocate a dummy node and you delete an entire…Sun, 30 Aug 2026 07:14:34 GMTLinked List Reversalguidehttps://dsa-grind.pages.dev/hashing-frequency-maps/pattern-guide/https://dsa-grind.pages.dev/hashing-frequency-maps/pattern-guide/Three skeletons cover nearly every hashing problem: count, seen-before, and prefix-sum + map.Sun, 30 Aug 2026 07:14:34 GMTHashing & Frequency Mapsguidehttps://dsa-grind.pages.dev/fast-and-slow-pointers/pattern-guide/https://dsa-grind.pages.dev/fast-and-slow-pointers/pattern-guide/One skeleton, three questions: is there a cycle, where does it start, what's the middle.Sun, 30 Aug 2026 07:14:34 GMTFast & Slow Pointersguidehttps://dsa-grind.pages.dev/sliding-window/pattern-guide/https://dsa-grind.pages.dev/sliding-window/pattern-guide/There are exactly two window templates. Decide first: is the window size fixed or variable? Everything else follows.Sun, 30 Aug 2026 07:14:34 GMTSliding Windowguidehttps://dsa-grind.pages.dev/two-pointers/pattern-guide/https://dsa-grind.pages.dev/two-pointers/pattern-guide/Memorise one skeleton. Every opposite-ends problem is this loop with the if/else body swapped.Sun, 30 Aug 2026 07:14:34 GMTTwo Pointersguidehttps://dsa-grind.pages.dev/stacks-and-queues/lc-622-design-circular-queue/https://dsa-grind.pages.dev/stacks-and-queues/lc-622-design-circular-queue/Wrap indices with % capacity to reuse freed slots. Track an explicit count so "full" and "empty" are never ambiguous.Sun, 30 Aug 2026 07:09:28 GMTStacks & Queuesproblemhttps://dsa-grind.pages.dev/stacks-and-queues/lc-994-rotting-oranges/https://dsa-grind.pages.dev/stacks-and-queues/lc-994-rotting-oranges/Everything rots simultaneously, so seed the queue with all rotten cells before the loop starts. BFS levels then equal elapsed minutes.Sun, 30 Aug 2026 07:09:28 GMTStacks & Queuesproblemhttps://dsa-grind.pages.dev/stacks-and-queues/lc-239-sliding-window-maximum/https://dsa-grind.pages.dev/stacks-and-queues/lc-239-sliding-window-maximum/An element that is smaller than a later element can never be the window max again — evict it immediately. What survives is a decreasing deque of indices…Sun, 30 Aug 2026 07:07:47 GMTStacks & Queuesproblemhttps://dsa-grind.pages.dev/stacks-and-queues/lc-232-implement-queue-using-stacks/https://dsa-grind.pages.dev/stacks-and-queues/lc-232-implement-queue-using-stacks/Reversing a stack into a second stack turns LIFO into FIFO. Only refill when the output stack is empty — that is what makes it amortised O(1) instead of O(n).Sun, 30 Aug 2026 07:06:57 GMTStacks & Queuesproblemhttps://dsa-grind.pages.dev/stacks-and-queues/lc-20-valid-parentheses/https://dsa-grind.pages.dev/stacks-and-queues/lc-20-valid-parentheses/The most recently opened bracket must be the first one closed — that is LIFO, so a stack does the matching for free.Sun, 30 Aug 2026 07:06:12 GMTStacks & Queuesproblemhttps://dsa-grind.pages.dev/monotonic-stack/lc-84-largest-rectangle-in-histogram/https://dsa-grind.pages.dev/monotonic-stack/lc-84-largest-rectangle-in-histogram/For each bar, the widest rectangle of that bar's height is bounded by the first strictly smaller bar on each side. A monotonic increasing stack finds both…Sun, 30 Aug 2026 07:05:22 GMTMonotonic Stackproblemhttps://dsa-grind.pages.dev/monotonic-stack/lc-496-next-greater-element-i/https://dsa-grind.pages.dev/monotonic-stack/lc-496-next-greater-element-i/Precompute every next-greater answer for nums2 in one O(n) pass, store it in a map, then answer each nums1 query in O(1).Sun, 30 Aug 2026 07:05:15 GMTMonotonic Stackproblemhttps://dsa-grind.pages.dev/monotonic-stack/lc-739-daily-temperatures/https://dsa-grind.pages.dev/monotonic-stack/lc-739-daily-temperatures/Keep a stack of indices whose answer is still unknown, in decreasing temperature order. A warmer day resolves several of them at once.Sun, 30 Aug 2026 07:04:06 GMTMonotonic Stackproblemhttps://dsa-grind.pages.dev/stacks-and-queues/pattern-guide/https://dsa-grind.pages.dev/stacks-and-queues/pattern-guide/One-line trigger: "Process in LIFO order (stack), FIFO order (queue), or maintain a running answer over a sliding window (deque)."Sun, 30 Aug 2026 07:03:18 GMTStacks & Queuesguidehttps://dsa-grind.pages.dev/monotonic-stack/pattern-guide/https://dsa-grind.pages.dev/monotonic-stack/pattern-guide/One-line trigger: "For each element, find the next / previous element that is greater / smaller."Sun, 30 Aug 2026 07:01:42 GMTMonotonic Stackguidehttps://dsa-grind.pages.dev/maang-prep/study-plan/https://dsa-grind.pages.dev/maang-prep/study-plan/Tailored for: Sanjay Naik — 3.5 yrs Java backend, microservices + GenAI healthcare exp Goal: Senior SWE / SDE-II / L4 / E4 offer Start: 2026-05-20 → Target…Sun, 30 Aug 2026 07:00:27 GMTMAANG Interview Prepnotehttps://dsa-grind.pages.dev/two-pointers/valid-palindrome/https://dsa-grind.pages.dev/two-pointers/valid-palindrome/Runnable Java file — no imports, no Maven needed. Save it and run java ValidPalindrome.java.Thu, 25 Jun 2026 20:41:08 GMTTwo Pointerscodehttps://dsa-grind.pages.dev/start-here/references/https://dsa-grind.pages.dev/start-here/references/All external links, articles, and resources used to build this DSA Study directory.Fri, 12 Jun 2026 07:40:30 GMTStart Herenotehttps://dsa-grind.pages.dev/blind-75/pattern-guide/https://dsa-grind.pages.dev/blind-75/pattern-guide/The Blind 75 is a curated list of 75 LeetCode problems created by Yangshun Tay in 2018. It covers the most frequently asked coding interview questions…Fri, 12 Jun 2026 07:40:30 GMTBlind 75guidehttps://dsa-grind.pages.dev/blind-75/graph/lc-133-clone-graph/https://dsa-grind.pages.dev/blind-75/graph/lc-133-clone-graph/Map each original node to its clone once, then wire neighbors by looking up clones in that map so you never duplicate nodes or get stuck in cycles.Fri, 12 Jun 2026 07:40:30 GMTBlind 75problemhttps://dsa-grind.pages.dev/blind-75/trie/lc-208-implement-trie/https://dsa-grind.pages.dev/blind-75/trie/lc-208-implement-trie/Each node holds links to 26 (or alphabet-sized) children and an isEnd flag; insert walks/creates edges; search/startsWith follow edges and check termination.Fri, 12 Jun 2026 07:40:30 GMTBlind 75problemhttps://dsa-grind.pages.dev/blind-75/string/lc-3-longest-substring-without-repeating/https://dsa-grind.pages.dev/blind-75/string/lc-3-longest-substring-without-repeating/For each right, move left just past the previous index of s[right] so the window never holds duplicates.Fri, 12 Jun 2026 07:40:30 GMTBlind 75problemhttps://dsa-grind.pages.dev/blind-75/tree/lc-104-maximum-depth-of-binary-tree/https://dsa-grind.pages.dev/blind-75/tree/lc-104-maximum-depth-of-binary-tree/The depth of a node is 1 + max(depth of left subtree, depth of right subtree); the base case is an empty subtree (depth 0).Fri, 12 Jun 2026 07:40:30 GMTBlind 75problemhttps://dsa-grind.pages.dev/blind-75/interval/lc-56-merge-intervals/https://dsa-grind.pages.dev/blind-75/interval/lc-56-merge-intervals/After sorting by start, each interval either extends the current merged block or starts a new one.Fri, 12 Jun 2026 07:40:30 GMTBlind 75problemhttps://dsa-grind.pages.dev/blind-75/heap/lc-23-merge-k-sorted-lists/https://dsa-grind.pages.dev/blind-75/heap/lc-23-merge-k-sorted-lists/Always pick the smallest current head among k lists using a min-heap ordered by node value (tie-break by list id).Fri, 12 Jun 2026 07:40:30 GMTBlind 75problemhttps://dsa-grind.pages.dev/blind-75/matrix/lc-73-set-matrix-zeroes/https://dsa-grind.pages.dev/blind-75/matrix/lc-73-set-matrix-zeroes/If matrix[i][j] == 0, row i and column j must become zero; store which rows/cols need clearing using O(1) extra space by repurposing the first row and first…Fri, 12 Jun 2026 07:40:30 GMTBlind 75problemhttps://dsa-grind.pages.dev/blind-75/array/lc-1-two-sum/https://dsa-grind.pages.dev/blind-75/array/lc-1-two-sum/Store each value’s index as you walk the array; the partner you need is target - current, which you can look up in O(1) with a map.Fri, 12 Jun 2026 07:40:30 GMTBlind 75problemhttps://dsa-grind.pages.dev/blind-75/dynamic-programming/lc-139-word-break/https://dsa-grind.pages.dev/blind-75/dynamic-programming/lc-139-word-break/A string is breakable if some prefix is a dictionary word and the remainder is also breakable—so you reuse answers for suffixes.Fri, 12 Jun 2026 07:40:30 GMTBlind 75problemhttps://dsa-grind.pages.dev/blind-75/tree/lc-124-binary-tree-maximum-path-sum/https://dsa-grind.pages.dev/blind-75/tree/lc-124-binary-tree-maximum-path-sum/At each node, the best path through that node uses the node plus at most one best “chain” from left and one from right; return to parent only a single…Fri, 12 Jun 2026 07:40:30 GMTBlind 75problemhttps://dsa-grind.pages.dev/blind-75/dynamic-programming/lc-377-combination-sum-iv/https://dsa-grind.pages.dev/blind-75/dynamic-programming/lc-377-combination-sum-iv/Distinct sequences count permutations: ways to reach sum t equals the sum over coins of ways to reach t - coin.Fri, 12 Jun 2026 07:40:30 GMTBlind 75problemhttps://dsa-grind.pages.dev/blind-75/graph/lc-207-course-schedule/https://dsa-grind.pages.dev/blind-75/graph/lc-207-course-schedule/If you can order all courses respecting prerequisites, the prerequisite graph is a DAG; if there is a cycle, some course depends on itself indirectly and…Fri, 12 Jun 2026 07:40:30 GMTBlind 75problemhttps://dsa-grind.pages.dev/blind-75/trie/lc-211-add-and-search-word/https://dsa-grind.pages.dev/blind-75/trie/lc-211-add-and-search-word/. matches any single letter — at a . node, try all non-null children recursively; otherwise follow the single matching edge.Fri, 12 Jun 2026 07:40:30 GMTBlind 75problemhttps://dsa-grind.pages.dev/blind-75/string/lc-424-longest-repeating-character-replacement/https://dsa-grind.pages.dev/blind-75/string/lc-424-longest-repeating-character-replacement/A window is valid if (window length) - (count of most frequent char) <= k — you only need to replace the “minority” characters.Fri, 12 Jun 2026 07:40:30 GMTBlind 75problemhttps://dsa-grind.pages.dev/blind-75/interval/lc-435-non-overlapping-intervals/https://dsa-grind.pages.dev/blind-75/interval/lc-435-non-overlapping-intervals/To fit maximum non-overlapping intervals, always keep the interval that ends earliest—it leaves the most room for the future.Fri, 12 Jun 2026 07:40:30 GMTBlind 75problem