dsa2 min read
Google — Count Inversions (Modified Merge Sort)
Count the number of inversions in an array (pairs where i < j but arr[i] > arr[j]) using modified merge sort in O(n log n). Google uses this to test deep algorithm understanding.
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Array
7 articles
dsa2 min read
Meta — Subarray Sum Equals K (Prefix Sum + HashMap)
Count subarrays with sum equal to k using prefix sums and a hashmap. O(n) time by tracking how many times each prefix sum has occurred.
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dsa2 min read
Amazon — Two Sum and Variants (HashMap, Sorted, 3Sum, 4Sum)
Comprehensive coverage of Two Sum, Two Sum II (sorted), 3Sum, and 4Sum. Amazon frequently tests these variants to gauge understanding of hashmap vs two-pointer trade-offs.
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dsa2 min read
Amazon — Find Median of Two Sorted Arrays (Binary Search)
Find the median of two sorted arrays in O(log(min(m,n))) time using binary search on partition points. A classic hard problem testing deep binary search understanding.
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dsa2 min read
Design Browser History — Stack-Based Navigation
Design a browser with visit, back, and forward navigation. Uses two stacks (or a doubly-ended array with pointer) for O(1) visit and O(steps) navigation.
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dsa2 min read
Design Circular Queue — Ring Buffer Implementation
Implement a circular queue (ring buffer) with fixed capacity supporting enQueue, deQueue, Front, Rear, isEmpty, and isFull in O(1) time using head and tail pointers.
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dsa1 min read
Design Parking System — Counter-Based Slot Management
Design a parking system with big, medium, and small spaces. O(1) addCar checks if space is available and decrements the counter, returning whether the car was parked.
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