Linked List Conditional Reversal

You are given a singly linked list of integers.

Task:

• Identify continuous segments of nodes such that:

  • The sum of values in that segment is even

• For each such segment:

  • Reverse the nodes within that segment

  • Keep the rest of the list unchanged

Important Rules:

• Each segment must be as large as possible while keeping the sum even

• All reversals must be done in-place

• Return the head of the modified linked list

📥 Input Format

• Head of a singly linked list

• Nodes are represented as: value → value → value → ...

📤 Output Format

• Modified linked list after performing required reversals

⚙️ Constraints

• 1≤N≤1000001 \le N \le 1000001≤N≤100000

• 1≤Node value≤100001 \le \text{Node value} \le 100001≤Node value≤10000

🧪 Examples

Example 1

Input:

1 → 2 → 3 → 4 → 5

Output:

1 → 2 → 3 → 4 → 5

Explanation: No large segment with even sum that benefits reversal.