92. Reverse Linked List II · Interview Problem

Leetcode

Medium

Linked Lists

Recursion

Stacks

Amazon

92. Reverse Linked List II

Reverse the nodes of a singly linked list between two given positions, inclusive, while keeping the rest of the list unchanged.

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Reverse Linked List II

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Primary

Problem Statement

Given the head of a singly linked list and two positions $left$ and $right$ , reverse the nodes from position $left$ to position $right$ in-place, using 1-based indexing.

All nodes outside the range $[left, right]$ must remain in their original relative order. The sublist between $left$ and $right$ should be reversed as a contiguous segment, and the final list should be returned.

Input Format

A singly linked list head
Two integers left and right with 1 <= left <= right <= n

The list nodes are provided in order.

Output Format

Return the head of the modified linked list after reversing the nodes in the specified range.

Constraints

The list contains at least one node
$1 \le left \le right \le n$
Reversal must be done by changing links between nodes; node values should not be modified as a substitute
Use $O(1)$ extra space if possible

Examples

Sample cases returned by the problem API.

Example 1

Input

head = [1,2,3,4,5], left = 2, right = 4

Output

[1,4,3,2,5]

Explanation

The sublist [2,3,4] is reversed to [4,3,2], while the rest of the list stays in place.

Example 2

Input

head = [5], left = 1, right = 1

Output

[5]

Explanation

A single-node sublist is unchanged.

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