Problema
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.
Vincoli
0 ≤ number of operations ≤ 10,000
−10^9 ≤ x ≤ 10^9
Esempi
Input:
operations = ["push_back 2", "push_front 1", "push_back 3", "reverse"]
Output atteso:
expected = [3, 2, 1]Input:
std::vector<std::string> operations = {"push_back 2", "push_front 1", "push_back 3", "reverse"};
Output atteso:
std::vector<long long> expected = {3, 2, 1};Input:
string[] operations = new string[] {"push_back 2", "push_front 1", "push_back 3", "reverse"};
Output atteso:
long[] expected = new long[] {3, 2, 1};Spiegazione
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"]
Output atteso:
expected = [5]Input:
std::vector<std::string> operations = {"push_back 5", "push_back 7", "push_back 5", "remove 5", "pop_front"};
Output atteso:
std::vector<long long> expected = {5};Input:
string[] operations = new string[] {"push_back 5", "push_back 7", "push_back 5", "remove 5", "pop_front"};
Output atteso:
long[] expected = new long[] {5};Spiegazione
remove takes out only the first 5, leaving 7 → 5; pop_front then removes 7: [5].
Come affrontarlo
Prova prima da solo, poi apri un suggerimento alla volta.
Suggerimento 1
A list type with cheap front and back inserts (std::list, LinkedList<T>, deque) does most of the work.
Suggerimento 2
remove deletes only the first match, and pop_front on an empty list does nothing.
Suggerimento 3
Reversing changes which end is the front for later pushes and pops.
Complessità attesa
O(n²) time, O(n) extra space
Riferimenti
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