Reverse a singly linked list in-place using three pointers
Three pointers (prev, curr, next) walk through the list, flipping each arrow backward
Initialize prev = null, curr = head. We will flip each arrow from curr to prev.
Three pointers (prev, curr, next) walk through the list, flipping each arrow backward
Initialize prev = null, curr = head. We will flip each arrow from curr to prev.
Save next = 2. Point 1→null. Move prev to 1, curr to 2.
Save next = 3. Point 2→1. Move prev to 2, curr to 3.
Save next = 4. Point 3→2. Move prev to 3, curr to 4.
Save next = 5. Point 4→3. Move prev to 4, curr to 5.
Point 5→4. curr becomes null, prev is the new head.