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Given a sorted dictionary of alien language, find the order of characters in the alien alphabet

Find all possible paths from source node to target node in a directed acyclic graph (DAG)

Find all articulation points in an undirected graph - vertices whose removal increases the number of connected components

Find shortest paths from a source vertex to all other vertices in a weighted graph, capable of handling negative edge weights

Learn BFS shortest path in an unweighted graph: O(V+E) time, queue + parent[] for path reconstruction. Step-by-step for interviews—start now.

Compute shortest distances from a start node in an undirected graph with uniform edge weight using BFS.

Determine if an array is sorted in ascending, descending, or not sorted at all

Create a deep copy of an undirected graph represented with adjacency lists

Connect ropes with minimum cost using greedy approach with heap

Determine if you can finish all courses given prerequisite relationships using topological sorting

Implement depth-first search traversal for graphs

Find all bridges (critical edges) in an undirected graph using Tarjan's algorithm

Find the duplicate number in an array containing n+1 integers where each integer is between 1 and n (inclusive)

Find the k largest elements from an unsorted array

Find the k smallest elements from an unsorted array

Design data structure to find median from continuous stream of integers

Find and return the largest element in an array of integers

Find and return the second largest element in an array of integers

Find shortest paths between all pairs of vertices in a weighted graph using dynamic programming

Find furthest building reachable using optimal allocation of bricks and ladders

Design and implement a stack data structure with push, pop, top, and empty operations

Check if a graph can be colored with exactly two colors such that no two adjacent nodes have the same color

Find the kth largest element in an unsorted array

Find kth smallest element in row and column sorted matrix using heap

Hard LC 84. Learn the O(n) monotonic stack (prev/next smaller) to compute max histogram area—step-by-step for FAANG interviews. Practice now.

Solve binary tree zig zag/spiral traversal with optimal BFS + deque. O(n) time, O(w) space. Step-by-step for interviews—practice now.

Find the longest palindromic substring in a given string

Find the length of the longest substring without repeating characters

Maximize array sum by flipping signs of k elements using greedy heap approach

Find minimum number of meeting rooms required using heap

Merge k sorted arrays into one sorted array using heap

LeetCode 88 merge sorted array in-place: reverse two pointers (merge from end) in O(m+n) time, O(1) space. Step-by-step + examples.

Design a stack that supports push, pop, top, and retrieving the minimum element in constant time

Find minimum refueling stops to reach target using greedy max-heap approach

Learn what a minimum spanning tree is + MST algorithm steps. Kruskal (Union-Find) O(E log E) vs Prim (heap) O(E log V). Practice now.

Find the minimum window substring that contains all characters of another string

Move all zeros in an array to the end while maintaining the relative order of non-zero elements

Find the time it takes for a signal to reach all nodes in a network using shortest path algorithms

Find minimum removals to reduce array size by half using greedy heap approach

Implement regular expression matching with support for '.' and '*'

Solve LC 767 with a greedy priority queue (max-heap). Learn the maxFreq ≤ ceil(n/2) condition + proof. O(n log k). Practice now.

Reverse the order of elements in an array in-place and return the modified array

Rotate an array to the right by k steps where k is non-negative

Find the minimum time for all oranges to rot using BFS

Serialize a binary tree to a string and deserialize it back to the original tree

Find the maximum element in each sliding window of size k

Hard LC 480: rolling median via sliding window + two heaps w/ lazy deletion. O(n log k) time, O(k) space. Step-by-step solution—prep now.

Find the smallest substring that contains all characters of a given pattern

Sort characters in string by frequency using heap or bucket sort

Calculate the span of stock prices for each day

Schedule tasks with cooling period using greedy approach with heap

Solve LeetCode 347 Top K Frequent Elements (Medium) with frequency map + bucket sort O(n) or min-heap O(n log k). Step-by-step for interviews.

Calculate how much rainwater can be trapped between bars of different heights

What is an ugly number? Solve n-th ugly number (2,3,5) with PriorityQueue + HashSet dedupe. O(n log n). Step-by-step—practice now.

Determine if two strings are anagrams of each other

Determine if the input string has valid brackets that are properly opened and closed

Traverse a binary tree vertically and return nodes by columns

Find the shortest transformation sequence from beginWord to endWord using single character changes