What is the preferred pattern for solving the Two Sum problem?
HashMap
This allows O(1) lookup to check if the complement exists.
What is the time complexity of the brute force approach for the Two Sum problem?
O(n²)
This involves checking every pair of numbers.
What is the preferred pattern for finding the length of the longest substring without repeating characters?
Sliding Window + Set
This allows for O(n) time complexity.
What is the time complexity of checking every substring for the longest substring without repeating characters?
O(n²)
This is inefficient compared to the sliding window approach.
What is the preferred pattern for checking if a string of brackets is properly balanced?
Stack
This follows Last-In-First-Out logic.
What is the time complexity for using a stack to check for balanced parentheses?
O(n)
This allows for efficient processing of brackets.
What is the preferred pattern for finding the maximum profit from buying and selling stock once?
Single Pass Tracking (greedy)
This allows for O(n) time complexity.
What is the time complexity of checking all buy/sell pairs for stock trading?
O(n²)
This is inefficient compared to the greedy approach.
What is the preferred pattern for finding the contiguous subarray with the largest sum?
Kadane’s Algorithm (Dynamic Programming)
This allows for O(n) time complexity.
What is the time complexity of checking all subarrays for the maximum subarray problem?
O(n²) or O(n³)
This is inefficient compared to Kadane’s Algorithm.
What is the preferred pattern for merging all overlapping intervals?
Sort + Greedy
This allows for O(n log n) time complexity.
What is the time complexity of merging intervals without sorting?
O(n²)
This is inefficient compared to the sorting approach.
What is the preferred pattern for visiting tree nodes level by level?
BFS with Queue
This ensures FIFO processing of nodes.
What is the time complexity of using DFS for level order traversal?
O(n)
BFS is more intuitive for level order.
What is the preferred pattern for counting the number of ways to climb stairs?
Dynamic Programming (Bottom-Up)
This builds from the bottom up.
What is the time complexity of a recursive approach without memoization for climbing stairs?
O(2^n)
This leads to recalculating the same stairs.
What is the preferred pattern for calculating the product of an array except self?
Prefix/Suffix Products
This avoids division and handles zeros.
What is the time complexity of using nested loops to calculate the product for each position?
O(n²)
This is inefficient compared to the prefix/suffix approach.
What is the preferred pattern for grouping anagrams?
HashMap with Sorted String as Key
This allows consistent representation of anagrams.
What is the time complexity of comparing every pair to check if they are anagrams?
O(n² × k)
This is inefficient compared to using a sorted string.
What is the preferred pattern for finding the K most frequent elements in an array?
HashMap (count) + Heap
This efficiently counts and retrieves top K elements.
What is the time complexity of sorting all frequencies to find the top K elements?
O(n log n)
Using a heap is more efficient.
What is the preferred pattern for counting connected components of 1s in a 2D grid?
DFS or BFS from each unvisited land cell
This explores entire islands.
What is the time complexity of checking adjacency for each cell without DFS/BFS?
O(n²m²)
This is inefficient compared to DFS/BFS.
