#35 Easy Time O(n) Space O(1) Animated

Reverse Linked List

Reverse a singly linked list.

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Tutor Mode Build the mental model before you memorize the code.

1 Predict
2 Trace
3 Explain
4 Implement

Pattern Pointer rewiring with saved next state

Before changing a link, save the only pointer that would otherwise be lost.

Approach: Iterative Pointer Reversal

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Core Insight

Before changing a link, save the only pointer that would otherwise be lost.

Common Pitfall

Always store next before redirecting current.next.

Description

Reverse a singly linked list.

Constraints

Time Complexity: O(n)
Space Complexity: O(1)

Solution — Iterative Pointer Reversal

TimeO(n) SpaceO(1)

Implementation Plan

Translate the invariant into these small, testable moves.

Initialize the pointers.
Save the next node.
Rewire the current node.
Advance both pointers until the list is consumed.

def reverseList(head):
    previous = None
    current = head
    while current:
        next_node = current.next
        current.next = previous
        previous = current
        current = next_node
    return previous

Merge Two Sorted Lists

Reverse Linked List

Steps

Description

Constraints

Tags

Solution — Iterative Pointer Reversal