#0169

Reverse a Linked List Represented as Pairs

MediumDSA25 min20 XP

Problem

Given a dictionary next_map where each key points to the next node or None, and a head, return the new head after reversing the list.

Why This Matters

Pointer reversal is the central linked-list operation; this version makes the pointer state visible without a custom class.

Function Signature

def reverse_next_map(next_map, head):

Examples

Example 1

Inputnext_map = {'A':'B','B':'C','C':None}, head='A'

Output'C'

After reversal C points to B, B points to A, and A points to None.

Constraints

Return the exact requested output.
Handle ordinary edge cases.
Prefer simple, interview-readable code.

CodePython

def reverse_next_map(next_map, head):
    """
    Input example: next_map = {'A':'B','B':'C','C':None}, head='A'
    Return: 'C'
    Return the value from the function so the tests can compare it. Do not print unless the prompt asks.
    """
    # write your code here
    return head

def reverse_next_map(next_map, head):
    """
    Input example: next_map = {'A':'B','B':'C','C':None}, head='A'
    Return: 'C'
    Return the value from the function so the tests can compare it. Do not print unless the prompt asks.
    """
    # write your code here
    return head

Visible browser tests run here when available.

Testcases1 visible / 3 hidden categories

Core example

Inputnext_map = {'A':'B','B':'C','C':None}, head='A'

Expected'C'

After reversal C points to B, B points to A, and A points to None.

Hidden Test Categories

empty or minimal inputduplicates or tieslarger input