Algorithm Library

Read input exactly as it is given and print only what is asked, in all four languages.

Count the work a program does and use the constraints to choose a plan that is fast enough.

Index, scan, reverse and rotate lists and strings without off-by-one errors.

Tally values with arrays and dictionaries to find modes, anagrams and equal pairs.

Put data in order, break ties on purpose, and let neighbours answer the question.

Answer many range totals with one subtraction, then handle range additions and grids.

Move two indices through sorted data or a window, and never step backwards.

Halve the search range at every step, and binary-search over the answer itself.

Try every combination with a recursive function that undoes each choice cleanly.

Take the locally best choice, and prove with an exchange argument when that is safe.

Explore graphs and grids, count steps from a start and find connected regions.

Merge groups and answer “same group?” almost instantly, then build a cheapest network.

Find cheapest routes with Dijkstra, all pairs with Floyd–Warshall, and extra states.

Define a state, a recurrence and an order, and fill a table instead of repeating work.

Knapsack items used once, tables over two strings, and DP over subsets as bitmasks.

Root a tree, total its subtrees, flatten them into intervals and find the diameter.

Keep range totals and minimums fast while the values keep changing.

Jump up a tree in powers of two to find ancestors, common ancestors and distances.

Group a directed graph into strongly connected components and work on the DAG between them.

Match patterns in linear time with the prefix function, and reason about borders and periods.