Graphs

Given an undirected unweighted graph with n nodes and edges, find shortest path length from source to target. Return -1 if unreachable.

Given a directed graph, determine if it contains a cycle.

Given n tasks and prerequisites [a,b] (b before a), return valid completion order. Empty array if impossible (cycle).

Given n nodes and edges, determine if graph is fully connected using Union-Find.

Given weighted directed graph, find shortest distances from source to all nodes. Return -1 for unreachable.

Given 2D grid of "1"s (land) and "0"s (water), count islands (4-directionally connected land).

Determine if undirected graph can be 2-colored with no same-color adjacent nodes.

Determine if graph can be colored with at most k colors such that no adjacent nodes share color.