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⚡Last Minute SWE DSA Revision
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⚡ Playlist

Top Last Minute SWE DSA Revision Interview Questions

Essential coding patterns to recognize and recall before interviews

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Hash MapStore values or frequencies for O(1) average lookup
Easy
PracticeVideo
Prefix SumConvert range queries into differences of prefix values
Medium
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Prefix XORUse XOR prefix values to cancel repeated elements
Medium
PracticeVideo
KadaneTrack the best subarray ending at the current position
Medium
PracticeVideo
Cyclic SortPlace each value at its correct index
Easy
PracticeVideo
Dutch National FlagMaintain low, middle and high regions
Medium
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Opposite PointersMove left/right based on whether the current value is too small or too large
Medium
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Same DirectionUse one pointer to scan and another to maintain the valid region
Easy
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Fast & SlowMove pointers at different speeds to detect structure
Easy
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Merge PointersCompare current elements and advance the smaller one
Easy
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Fixed WindowAdd the new element and remove the element leaving the window
Easy
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Variable WindowExpand until invalid, then shrink until valid
Medium
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Frequency WindowMaintain frequencies and track when the window satisfies the requirement
Hard
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Window Max / MinUse a monotonic deque to keep useful candidates
Hard
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Classic SearchDiscard half of the search space each step
Easy
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Lower / Upper BoundBinary search for the boundary rather than an exact value
Medium
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Rotated SearchIdentify which half is sorted and decide where the target can exist
Medium
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Peak SearchUse slope direction to eliminate half the array
Medium
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Search on AnswerBinary search the answer and check whether a candidate is feasible
Medium
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ReverseMaintain previous, current and next pointers
Easy
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Fast & SlowUse two pointers moving at different speeds
Easy
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MergeCompare nodes and connect the smaller node
Easy
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Split → Reverse → MergeSplit the list, reverse one half, then merge both halves
Medium
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Cache DesignCombine HashMap with doubly linked list
Medium
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StackLast in, first out
Easy
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Monotonic StackMaintain an increasing or decreasing stack of useful candidates
Medium
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QueueProcess elements in arrival order
Medium
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Monotonic DequeRemove dominated elements while preserving useful candidates
Hard
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Merge IntervalsSort by start and merge whenever intervals overlap
Medium
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Interval SchedulingUsually sort by ending time and greedily choose the earliest finish
Medium
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Meeting SchedulingSort events or use a min-heap to track active meetings
Medium
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Sweep LineConvert intervals into sorted start/end events
Medium
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Top KMaintain only the K most useful candidates with a heap
Medium
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Two HeapsMax-heap for lower half and min-heap for upper half
Hard
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Merge KHeap stores the smallest current element from each source
Hard
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Heap SchedulingUse a heap to dynamically select the next candidate
Hard
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Tree DFSSolve children first and combine their results
Easy
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Tree BFSProcess nodes level by level with a queue
Medium
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Tree PathReturn useful information upward while updating the global answer
Hard
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BSTLeft < Root < Right; inorder traversal is sorted
Medium
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Lowest Common AncestorFind where the paths to the two nodes split
Medium
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Tree ConstructionUse one traversal to identify the root and another to divide subtrees
Medium
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Serialize / DeserializeEncode structure and null nodes so the exact tree can be reconstructed
Hard
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Graph DFSVisit deeply while tracking visited nodes
Medium
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Graph BFSFirst visit to a node gives its shortest distance
Medium
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Grid BFS / DFSTreat cells as graph nodes and explore four/eight directions
Easy
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Multi-Source BFSPut all sources into the queue initially
Medium
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Topological SortOrder nodes so every dependency appears before its dependent
Medium
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Union FindTrack connected components with parent and rank/size
Medium
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DijkstraRepeatedly finalize the currently closest node
Medium
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Bellman-FordRelax all edges repeatedly
Medium
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Floyd-WarshallAllow each node to become an intermediate point
Medium
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Minimum Spanning TreeUse Prim or Kruskal to select minimum-cost edges without cycles
Medium
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BridgesUse DFS low-link times to identify critical edges
Hard
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SubsetsChoose → explore → undo
Medium
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PermutationsChoose an unused element at each position
Medium
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CombinationsExplore choices while controlling the starting index
Medium
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Grid BacktrackingMark → explore → unmark
Medium
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Constraint SearchTry a candidate, prune invalid states, then backtrack
Hard
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Local BestChoose the locally optimal option and prove it cannot hurt the future
Medium
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Greedy + SortingSort first, then repeatedly make the optimal local choice
Medium
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Greedy + HeapUse a heap to always access the best current option
Medium
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1D DPDefine state → transition → base case
Easy
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Grid DPBuild each cell from previously solved neighboring cells
Medium
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0/1 KnapsackState represents position and remaining capacity/target
Medium
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Unbounded KnapsackAllow the same item to contribute multiple times
Medium
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LISTrack the best increasing sequence ending at each position
Medium
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LCSIf characters match, advance both; otherwise try skipping one
Medium
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String DPState usually represents positions in one or two strings
Medium
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Interval DPTry every partition point and combine subinterval answers
Hard
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Stock DPState = day + holding status + transaction state
Medium
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String HashingRepresent strings using counts or hashable signatures
Medium
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PalindromeCompare from both ends or expand around a center
Medium
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String WindowExpand/shrink while maintaining character frequencies
Medium
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String StackUse stack to remember unresolved characters
Medium
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KMPReuse previously matched prefix information
Easy
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TrieStore characters along paths for fast prefix operations
Medium
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XORa ^ a = 0 and a ^ 0 = a
Easy
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Bit TricksUse shifts, masks and bit operations instead of arithmetic loops
Easy
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BitmaskUse each bit to represent whether an element/state is active
Medium
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GCDUse Euclid's algorithm
Easy
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Modular ArithmeticPerform operations while keeping values reduced modulo M
Medium
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Fast PowerExponentiation by squaring in O(log n)
Medium
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SieveMark multiples of each prime
Medium
PracticeVideo