What is the time complexity of reverse a linked list?

Worst case O(n). Space complexity is O(1).

Reverse a linked list

medium

Saving `next` before overwriting `curr.next` is not defensive coding - it is mandatory. Swap those two lines and the rest of the list becomes unreachable.

Worst O(n)Space O(1)

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Where to go next

Singly linked list

easy

O(1) at the head, a walk for everything else.

Floyd's cycle detection

medium

Tortoise and hare, in O(1) memory.

Two pointers

easy

One comparison eliminates a whole row of the brute force.