One Shared Configuration

Simulate a singleton settings object: every part of the program reads and writes the same instance.

このチャレンジで学べること

Share one object across the whole program
Create an instance lazily on first use
Read and update settings through one place

問題

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, or missing if 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.

制約

1 ≤ number of operations ≤ 10,000

Keys and values have 1 to 20 characters

例

例 1

入力：
operations = ["set theme dark", "get theme", "get language"]

期待される出力：
expected = ["dark", "missing"]

入力：
std::vector<std::string> operations = {"set theme dark", "get theme", "get language"};

期待される出力：
std::vector<std::string> expected = {"dark", "missing"};

入力：
string[] operations = new string[] {"set theme dark", "get theme", "get language"};

期待される出力：
string[] expected = new string[] {"dark", "missing"};

解説

theme was set to dark; language was never set, so it is missing: ["dark", "missing"].

例 2

入力：
operations = ["set lang en", "set lang vi", "get lang"]

期待される出力：
expected = ["vi"]

入力：
std::vector<std::string> operations = {"set lang en", "set lang vi", "get lang"};

期待される出力：
std::vector<std::string> expected = {"vi"};

入力：
string[] operations = new string[] {"set lang en", "set lang vi", "get lang"};

期待される出力：
string[] expected = new string[] {"vi"};

解説

The second set replaces the first value in the same shared instance: ["vi"].

解き方のヒント

まずは自分で考えてから、ヒントを 1 つずつ開いてみましょう。

ヒント 1

All operations read and write the same single object.

ヒント 2

A dictionary from key to value is enough to hold the settings.

ヒント 3

A key that was never set must return the text missing.

目安の計算量

O(number of operations) time, O(number of keys) extra space

参考資料

この課題はCodeUtility用に調整されています。上記の説明と制約に従ってください。