What is the time complexity of topological sort?

Worst case O(V + E). Space complexity is O(V).

Topological sort

medium

Indegree zero means nothing is waiting on this. If the queue empties while vertices remain, those vertices are waiting on each other - a cycle, detected with no extra check.

Worst O(V + E)Space O(V)

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Where to go next

Depth-first search

easy

A stack instead of a queue - that is the only difference.

Breadth-first search

easy

Expands in rings, so it finds shortest paths.

Union-Find (disjoint set)

medium

Path compression and union by rank, together.