Problem
A linked list stores values in nodes that point to the next node, so adding or removing at the front is cheap. Simulate one that starts empty.
Process the operations in order:
push_front x: add x at the front.push_back x: add x at the back.pop_front: remove the first value (ignored when the list is empty).remove x: remove the first node whose value is x, if there is one.reverse: reverse the order of the nodes.
Implement linked_list_operations(operations).
Input
operations: The operations.
Output
Return the values in the list from front to back.
Constraints
0 ≤ number of operations ≤ 10,000
−10^9 ≤ x ≤ 10^9
Examples
Input:
operations = ["push_back 2", "push_front 1", "push_back 3", "reverse"]
Expected output:
expected = [3, 2, 1]Input:
std::vector<std::string> operations = {"push_back 2", "push_front 1", "push_back 3", "reverse"};
Expected output:
std::vector<long long> expected = {3, 2, 1};Input:
string[] operations = new string[] {"push_back 2", "push_front 1", "push_back 3", "reverse"};
Expected output:
long[] expected = new long[] {3, 2, 1};Explanation
The list grows to 1 → 2 → 3, and reversing it gives [3, 2, 1].
Input:
operations = ["push_back 5", "push_back 7", "push_back 5", "remove 5", "pop_front"]
Expected output:
expected = [5]Input:
std::vector<std::string> operations = {"push_back 5", "push_back 7", "push_back 5", "remove 5", "pop_front"};
Expected output:
std::vector<long long> expected = {5};Input:
string[] operations = new string[] {"push_back 5", "push_back 7", "push_back 5", "remove 5", "pop_front"};
Expected output:
long[] expected = new long[] {5};Explanation
remove takes out only the first 5, leaving 7 → 5; pop_front then removes 7: [5].
How to approach it
Try on your own first, then open one hint at a time.
Hint 1
A list type with cheap front and back inserts (std::list, LinkedList<T>, deque) does most of the work.
Hint 2
remove deletes only the first match, and pop_front on an empty list does nothing.
Hint 3
Reversing changes which end is the front for later pushes and pops.
Expected complexity
O(n²) time, O(n) extra space
References
This challenge is adapted for CodeUtility. Follow the statement and constraints above.