Symmetric Bead String

Easy

Beads are threaded on a string, and each bead carries a digit. The string is given as the singly linked list head, one node per bead. Return True if the digits read the same from the start and from the end of the string, and False otherwise. Copying the values into an array is the easy way; try to use only O(1) extra memory.

Example 1

head=list_node([4, 7, 1, 7, 4]) → True

The beads read the same from either end: 4, 7, 1, 7, 4.

Example 2

head=list_node([3, 3, 5]) → False

Left to right it is 3, 3, 5; right to left it is 5, 3, 3. Not symmetric.

Example 3

head=list_node([8]) → True

Constraints

The list has between 1 and 10⁵ nodes
0 ≤ Node.val ≤ 9

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Topics

Stack Recursion Linked List Two Pointers

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Input

head=list_node([4, 7, 1, 7, 4])

Expected

True

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