Lesson 185
Fast & Slow Pointers
Floyd's Tortoise & Hare
1:00How to detect cycles, find list midpoints, and locate cycle entry nodes using two pointers moving at different speeds — Floyd's Tortoise and Hare algorithm.
By the end, you can
- Explain why two pointers moving at speeds 1 and 2 are guaranteed to meet inside any cycle.
- Trace the hasCycle algorithm step by step and identify the meeting node.
- Describe the a = c theorem and apply the phase-two reset to find a cycle's entry node.
- Predict which node slow returns on after the middle-finding loop for both odd- and even-length lists.
- Recognize implicit linked-list structure in non-list problems such as Happy Number.
- State the time and space complexity of the fast/slow pattern and compare it to the hash-set alternative.
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