Implement `reverse_k_group(values, k)` for a singly linked list represented by the array `values` in traversal order. Reverse every consecutive group of exactly `k` nodes and return the resulting values. If fewer than `k` nodes remain at the end, preserve their original order. You may change links between existing nodes in a linked-list implementation, but not node values. ### Constraints - `0 <= len(values) <= 200000` - `1 <= k <= 200000` - `-10^9 <= values[i] <= 10^9` - Target `O(n)` time and `O(1)` auxiliary pointer space, excluding the returned array representation. ### Examples - `[1, 2, 3, 4, 5]`, `k = 2` returns `[2, 1, 4, 3, 5]`. - `[1, 2, 3, 4, 5]`, `k = 3` returns `[3, 2, 1, 4, 5]`. - `[1, 2]`, `k = 1` returns `[1, 2]`. ```hint Confirm the group before changing it Locate the kth node from the predecessor of the current group. If it does not exist, stop without modifying the suffix. ``` ```hint Preserve the connections around a reversal Track the node before the group, the original first node, and the first node after the group. ```