Problema
The singleton pattern makes sure a class has exactly one instance that everyone shares, a common choice for application settings.
Simulate one shared configuration that starts empty. Process the operations in order:
set <key> <value>: store the value for the key (replacing any old value).get <key>: read the key's current value, ormissingif it was never set.
Because every caller uses the same instance, a value set by one operation is visible to every later get.
Implement shared_configuration(operations).
Input
operations: Strings in the two forms above. Keys and values contain no spaces.
Output
Return the results of the get operations, in order.
Vincoli
1 ≤ number of operations ≤ 10,000
Keys and values have 1 to 20 characters
Esempi
Input:
operations = ["set theme dark", "get theme", "get language"]
Output atteso:
expected = ["dark", "missing"]Input:
std::vector<std::string> operations = {"set theme dark", "get theme", "get language"};
Output atteso:
std::vector<std::string> expected = {"dark", "missing"};Input:
string[] operations = new string[] {"set theme dark", "get theme", "get language"};
Output atteso:
string[] expected = new string[] {"dark", "missing"};Spiegazione
theme was set to dark; language was never set, so it is missing: ["dark", "missing"].
Input:
operations = ["set lang en", "set lang vi", "get lang"]
Output atteso:
expected = ["vi"]Input:
std::vector<std::string> operations = {"set lang en", "set lang vi", "get lang"};
Output atteso:
std::vector<std::string> expected = {"vi"};Input:
string[] operations = new string[] {"set lang en", "set lang vi", "get lang"};
Output atteso:
string[] expected = new string[] {"vi"};Spiegazione
The second set replaces the first value in the same shared instance: ["vi"].
Come affrontarlo
Prova prima da solo, poi apri un suggerimento alla volta.
Suggerimento 1
All operations read and write the same single object.
Suggerimento 2
A dictionary from key to value is enough to hold the settings.
Suggerimento 3
A key that was never set must return the text missing.
Complessità attesa
O(number of operations) time, O(number of keys) extra space
Riferimenti
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