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Hello Python

Relink Nodes Safely

Practice ExerciseInterviewEasyLinked List

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Problem

Implement bypass_linked_node(next_indices, remove_index). next_indices[i] is the next node index or -1. Return a new next-index list in which the unique predecessor of remove_index points to the removed node’s successor. If removing the head at index 0, just return the copied links with no predecessor update.

Starter code

def bypass_linked_node(next_indices, remove_index):
    pass
Test cases

remove-middle

{
  "args": [
    [
      1,
      2,
      3,
      -1
    ],
    2
  ]
}

Expected: [1,3,3,-1]

remove-tail

{
  "args": [
    [
      1,
      2,
      -1
    ],
    2
  ]
}

Expected: [1,-1,-1]

Wizard outline
  1. Step 1: Copy state and preserve a removed head

    Return an independent copy when remove_index is the head boundary used by this representation. Copying first prevents the focused relink operation from mutating the caller input.

  2. Step 2: Find and detach a tail predecessor

    Locate the unique index whose next link points at a removed tail and redirect it to -1. A tail removal isolates predecessor ownership without yet following a successor link.

  3. Step 3: Redirect the predecessor to the successor

    Generalize the tail case so the predecessor receives whatever successor the removed node stored. Middle and nonlinear storage cases differ only in the successor value assigned to that one incoming edge.

Footguns and prerequisites
  • Redirecting the removed node itself does not bypass it from the reachable chain.
  • Mutating next_indices violates the requirement to return a copied representation.
  • linked lists
Reviewed references
Prepared Interview Problems
  • Add Two Numbers(opens in a new tab)

    Relink Nodes Safely isolates every untouched node keeps its original next link, and at most one predecessor changes to the removed node’s former successor. That focused state discipline is required when implementing add two numbers as a complete Interview Problem.

  • Insert GCD Nodes in a Linked List(opens in a new tab)

    Relink Nodes Safely isolates every untouched node keeps its original next link, and at most one predecessor changes to the removed node’s former successor. That focused state discipline is required when implementing insert gcd linked list as a complete Interview Problem.

  • Insert Into a Sorted Circular List(opens in a new tab)

    Relink Nodes Safely isolates every untouched node keeps its original next link, and at most one predecessor changes to the removed node’s former successor. That focused state discipline is required when implementing insert sorted circular values as a complete Interview Problem.

  • LRU Cache(opens in a new tab)

    Relink Nodes Safely isolates every untouched node keeps its original next link, and at most one predecessor changes to the removed node’s former successor. That focused state discipline is required when implementing lru cache as a complete Interview Problem.

  • Odd Even Linked List(opens in a new tab)

    Relink Nodes Safely isolates every untouched node keeps its original next link, and at most one predecessor changes to the removed node’s former successor. That focused state discipline is required when implementing odd even linked list as a complete Interview Problem.

  • Remove Nth Node From End(opens in a new tab)

    Relink Nodes Safely isolates every untouched node keeps its original next link, and at most one predecessor changes to the removed node’s former successor. That focused state discipline is required when implementing remove nth node from end as a complete Interview Problem.

  • Reorder List(opens in a new tab)

    Relink Nodes Safely isolates every untouched node keeps its original next link, and at most one predecessor changes to the removed node’s former successor. That focused state discipline is required when implementing reorder list as a complete Interview Problem.

  • Split Linked List in Parts(opens in a new tab)

    Relink Nodes Safely isolates every untouched node keeps its original next link, and at most one predecessor changes to the removed node’s former successor. That focused state discipline is required when implementing split linked list parts as a complete Interview Problem.

Recommended approach and implementation

Linked-list edits change relationships between nodes; preserve the successor before redirecting the predecessor link. Every untouched node keeps its original next link, and at most one predecessor changes to the removed node’s former successor.

Why it works: Copying the next-index array preserves the original array and every existing link. When remove_index is not the head, replacing its unique predecessor entry with links[remove_index] rewires that predecessor to the removed node’s successor without deleting or reordering any array entry.

def bypass_linked_node(next_indices, remove_index):
    links = next_indices.copy()
    if remove_index == 0:
        return links
    for index, next_index in enumerate(links):
        if next_index == remove_index:
            links[index] = links[remove_index]
            break
    return links