Problema
A to-do app keeps tasks in a typed collection such as List<T>. Each task has a title and a done flag.
Start with an empty list and process the operations, each a command and a title (the title is everything after the first space):
add <title>: add a pending task at the end, unless a task with that title already exists.done <title>: mark that task as done (no effect if it does not exist).remove <title>: delete that task (no effect if it does not exist).
Implement todo_list(operations).
Input
operations: The operations. Titles may contain spaces and are compared exactly.
Output
Return the titles of the tasks that are not done, in the order they were added.
Vincoli
0 ≤ number of operations ≤ 10,000
Titles have 1 to 50 characters
Esempi
Input:
operations = ["add Buy milk", "add Write report", "done Buy milk", "add Call Ada"]
Output atteso:
expected = ["Write report", "Call Ada"]Input:
std::vector<std::string> operations = {"add Buy milk", "add Write report", "done Buy milk", "add Call Ada"};
Output atteso:
std::vector<std::string> expected = {"Write report", "Call Ada"};Input:
string[] operations = new string[] {"add Buy milk", "add Write report", "done Buy milk", "add Call Ada"};
Output atteso:
string[] expected = new string[] {"Write report", "Call Ada"};Spiegazione
Buy milk is done, so only the other two remain, in the order they were added: ["Write report", "Call Ada"].
Input:
operations = ["add Gym", "add Gym", "remove Gym", "done Gym"]
Output atteso:
expected = []Input:
std::vector<std::string> operations = {"add Gym", "add Gym", "remove Gym", "done Gym"};
Output atteso:
std::vector<std::string> expected = {};Input:
string[] operations = new string[] {"add Gym", "add Gym", "remove Gym", "done Gym"};
Output atteso:
string[] expected = new string[] {};Spiegazione
The second add is ignored because Gym already exists; removing it leaves nothing, and done on a missing task does nothing: [].
Come affrontarlo
Prova prima da solo, poi apri un suggerimento alla volta.
Suggerimento 1
Store each task as a small record of title and done.
Suggerimento 2
Look a task up by its exact title before adding, completing or removing it.
Suggerimento 3
At the end keep only the tasks that are not done, in insertion order.
Complessità attesa
O(n²) time, O(n) extra space
Riferimenti
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