Swap With the Mirror Position

Medium

You are given a singly linked list head and an integer pos. Find the pos-th node from the start and the pos-th node from the end (both counted from 1), and swap their values. Return the head of the list.

Example 1

head=list_node([3, 6, 9, 12, 15, 18]), pos=2 → [3, 15, 9, 12, 6, 18]

The second node from the front holds 6 and the second from the back holds 15, so their values are exchanged.

Example 2

head=list_node([5, 1, 7]), pos=2 → [5, 1, 7]

The second node from the front and from the back is the same node, so the list does not change.

Example 3

head=list_node([40, 50]), pos=1 → [50, 40]

The first from the front is 40 and the first from the back is 50, so they swap.

Constraints

The list has n nodes
1 ≤ pos ≤ n ≤ 10⁵
0 ≤ Node.val ≤ 100

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Topics

Linked List Two Pointers

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Input

head=list_node([3, 6, 9, 12, 15, 18]), pos=2

Expected

[3, 15, 9, 12, 6, 18]

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