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Data Structures and Algorithms Linked List

Detect Loop

Lesson 14/65

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Linked List Algorithms - Loop Detection

Detect Loop

Detect Loop uses slow and fast pointers; if the fast pointer laps the slow pointer, the list contains a cycle.

TimeO(n)

SpaceO(1)

Try Interactive Simulator

Two Speeds

Slow moves one link while fast moves two links.

Meeting Means Cycle

In a loop, fast eventually catches slow.

Null Means Safe

If fast reaches null, the list has no cycle.

No Extra Set

Floyd-style detection avoids storing visited nodes.

List valuesSelected value

Click a node to select itDrag nodes to reposition the chainDrag panel headers to rearrange toolsResize panel corners when space gets tight

Current Step

Place slow and fast at head.

Speed