Data Structures

Shortest paths in weighted graphs, in algorithms: Dijkstra's algorithm, Bellman-Ford and Floyd-Warshall, and how weights and pairs choose between them.

Intermediate to Advanced11 cards · 6 qnot started

Breadth-first and depth-first search in algorithms, and what they find: components, cycles, bipartite graphs and unweighted shortest paths.

Intermediate to Advanced10 cards · 6 qnot started

Minimum spanning trees in algorithms: the cut property, Kruskal's algorithm with union-find, Prim's algorithm with a heap, and why neither gives shortest paths.

Intermediate to Advanced9 cards · 4 qnot started

Graph representations: storing vertices and edges as an adjacency list or an adjacency matrix, and choosing between them by how many edges there are.

Beginner to Intermediate8 cards · 4 qnot started

Ordering tasks so every dependency comes first, in algorithms: Kahn's algorithm, depth-first finishing times, and how each one finds a cycle.

Intermediate to Advanced8 cards · 4 qnot started

Grid traversal: treating a grid of cells as a graph for breadth-first and depth-first search, flood fills and searches from many starting cells.

Intermediate to Advanced8 cards · 4 qnot started

Graph modelling: finding the vertices and edges hidden in a problem's wording, then solving it with a search, a topological sort or union-find.

Intermediate to Advanced8 cards · 4 qnot started

Union-find in data structures: tracking which items share a group with a parent array, merging groups, and counting components and detecting cycles in a graph.

Intermediate to Advanced7 cards · 3 qnot started

Graph connectivity in algorithms: strongly connected components with Kosaraju's two passes, bridges and articulation points from low values, and choosing the tool.

Intermediate to Advanced7 cards · 3 qnot started

The Java Collections Framework: List, Set and Queue, what each promises, and which type to declare a variable with.

Intermediate to Advanced8 cards · 5 qnot started

ArrayList vs LinkedList: two lists with the same methods and opposite costs, how an ArrayList grows, and removing while iterating.

Intermediate to Advanced8 cards · 6 qnot started

Sets and queues: collections that decide what counts as a duplicate and what comes out next, and which class to use.

Intermediate to Advanced8 cards · 5 qnot started

How a HashMap works: hashing to a bucket, collisions, resizing, the three map classes, and null keys.

Intermediate to Advanced9 cards · 5 qnot started

Java arrays: a fixed run of values under one name, creating and filling one, zero-based indexes, and why an array cannot grow.

Beginner to Intermediate8 cards · 5 qnot started

Java equals, hashCode and toString: the defaults every object inherits, the contract between equals and hashCode, and how hash maps lose keys.

Intermediate to Advanced8 cards · 6 qnot started

Sorting your own types in Java: Comparable for the natural order, Comparator for the rest, and the two ways a comparator goes wrong.

Intermediate to Advanced9 cards · 5 qnot started

Java streams: pipelines over a source, lazy evaluation, map and flatMap, collectors, single use, and when parallel streams pay.

Intermediate to Advanced10 cards · 6 qnot started

Arrays and strings: why reading by index is instant, why inserting in the middle is not, and how a dynamic array grows without slowing every append.

Beginner to Intermediate9 cards · 4 qnot started

Java arrays: a fixed run of values under one name, creating and filling one, zero-based indexes, and why an array cannot grow.

Beginner to Intermediate8 cards · 5 qnot started

Prefix sums: precomputing running totals so any range sum is one subtraction, and counting the runs that hit a target with a hash map.

Intermediate to Advanced8 cards · 4 qnot started

Grid traversal: treating a grid of cells as a graph for breadth-first and depth-first search, flood fills and searches from many starting cells.

Intermediate to Advanced8 cards · 4 qnot started

ArrayList vs LinkedList: two lists with the same methods and opposite costs, how an ArrayList grows, and removing while iterating.

Intermediate to Advanced8 cards · 6 qnot started

Java generics: type parameters, what the compiler checks, type erasure, wildcards, and what erasure forbids.

Intermediate to Advanced9 cards · 5 qnot started

Binary Search Trees: keeping keys in order so that search, insert and delete each follow one path, and why insertion order decides the cost.

Beginner to Advanced9 cards · 6 qnot started

Heaps: a complete binary tree stored in an array that always gives the smallest or largest item first, the data structure behind every priority queue.

Beginner to Intermediate9 cards · 5 qnot started

Binary Trees: naming the parts of a tree, traversing it in four orders, counting height in edges, and writing functions that combine two subtrees' answers.

Beginner to Intermediate8 cards · 4 qnot started

Tree patterns: solving binary tree problems by passing values down or returning them up, level by level, or through both subtrees at once.

Intermediate to Advanced8 cards · 4 qnot started

Tries: a tree with one node per letter, which answers whether any stored word starts with a prefix in time that ignores how many words there are.

Beginner to Intermediate7 cards · 3 qnot started

Linked lists: nodes joined by references, so inserting and deleting is a rewire instead of a shift, at the price of reading by position.

Beginner to Intermediate9 cards · 4 qnot started

Fast and slow pointers: two pointers moving at different speeds that find a list's middle, detect a cycle and locate where the cycle starts.

Intermediate to Advanced8 cards · 4 qnot started

Linked list reversal: reversing a linked list in place with three references, and reversing part of a list or groups of nodes with a dummy node.

Intermediate to Advanced8 cards · 4 qnot started

Merge sort: the sorting algorithm that splits an array in half, sorts each half and merges them, in O(n log n) time on every input.

Intermediate8 cards · 4 qnot started

Hash tables: the data structure that turns a key into an array index to find values in expected constant time, and what collisions, growth and bad keys do to it.

Beginner to Intermediate10 cards · 6 qnot started

How a HashMap works: hashing to a bucket, collisions, resizing, the three map classes, and null keys.

Intermediate to Advanced9 cards · 5 qnot started

Hash map patterns: complements, counts and canonical keys that turn a search inside a loop into one lookup, and the array used as its own hash map.

Intermediate to Advanced8 cards · 4 qnot started

Java equals, hashCode and toString: the defaults every object inherits, the contract between equals and hashCode, and how hash maps lose keys.

Intermediate to Advanced8 cards · 6 qnot started

Stacks and queues: the two data structures defined by the order items leave in, last in first out or first in first out, and how to build each cheaply.

Beginner to Intermediate9 cards · 4 qnot started

Monotonic stack: finding the next greater or smaller element of every position in one pass, with a stack kept in order.

Intermediate to Advanced8 cards · 4 qnot started

Sets and queues: collections that decide what counts as a duplicate and what comes out next, and which class to use.

Intermediate to Advanced8 cards · 5 qnot started

Heap patterns: keeping the top K items, merging sorted lists and tracking a running median with one heap or two.

Intermediate to Advanced8 cards · 4 qnot started