2691. 不可变辅助工具 🔒
2691. 不可变辅助工具 🔒
题目
Creating clones of immutable objects with minor alterations can be a tedious process. Write a class ImmutableHelper
that serves as a tool to help with this requirement. The constructor accepts an immutable object obj
which will be a JSON object or array.
The class has a single method produce
which accepts a function mutator
. The function returns a new object which is similar to the original except it has those mutations applied.
mutator
accepts a proxied version of obj
. A user of this function can (appear to) mutate this object, but the original object obj
should not actually be effected.
For example, a user could write code like this:
const originalObj = { x: 5 };
const helper = new ImmutableHelper(originalObj);
const newObj = helper.produce((proxy) => {
proxy.x = proxy.x + 1;
});
console.log(originalObj); // {"x": 5}
console.log(newObj); // {"x": 6}
Properties of the mutator
function:
- It will always return
undefined
. - It will never access keys that don't exist.
- It will never delete keys (
delete obj.key
) - It will never call methods on a proxied object (
push
,shift
, etc). - It will never set keys to objects (
proxy.x = {}
)
Note on how the solution will be tested: the solution validator will only analyze differences between what was returned and the original obj
. Doing a full comparison would be too computationally expensive. Also, any mutations to the original object will result in a wrong answer.
Example 1:
Input:
obj = {"val": 10},
mutators = [
proxy => { proxy.val += 1; },
proxy => { proxy.val -= 1; }
]
Output:
[{"val": 11}, {"val": 9}]
Explanation:
const helper = new ImmutableHelper({ val: 10 });
helper.produce((proxy) => {
proxy.val += 1;
}); // { "val": 11 }
helper.produce((proxy) => {
proxy.val -= 1;
}); // { "val": 9 }
Example 2:
Input:
obj = {"arr": [1, 2, 3]}
mutators = [
proxy => {
proxy.arr[0] = 5;
proxy.newVal = proxy.arr[0] + proxy.arr[1];
}
]
Output:
[{"arr": [5, 2, 3], "newVal": 7 }]
Explanation: Two edits were made to the original array. The first element in the array was to set 5. Then a new key was added with a value of 7.
Example 3:
Input:
obj = {"obj": {"val": {"x": 10, "y": 20}}}
mutators = [
proxy => {
let data = proxy.obj.val;
let temp = data.x;
data.x = data.y;
data.y = temp;
}
]
Output:
[{"obj": {"val": {"x": 20, "y": 10}}}]
Explanation: The values of "x" and "y" were swapped.
Constraints:
2 <= JSON.stringify(obj).length <= 4 * 10^5
mutators
is an array of functionstotal calls to produce() < 10^5
题目大意
创建带有微小修改的不可变对象的克隆副本是一个繁琐的过程。请你编写一个名为 ImmutableHelper
的类,作为满足这一要求的工具。构造函数接受一个不可变对象 obj
,该对象将是一个 JSON 对象或数组。
该类有一个名为 produce
的方法,它接受一个名为 mutator
的函数。该函数返回一个新的对象,它与原始对象相似,但应用了这些变化。
mutator
函数接受 obj
的 代理 版本。函数的使用者可以(看起来)对该对象进行修改,但原始对象 obj
实际上没有被改变。
const originalObj = { x: 5 };
const helper = new ImmutableHelper(originalObj);
const newObj = helper.produce((proxy) => {
proxy.x = proxy.x + 1;
});
console.log(originalObj); // {"x": 5}
console.log(newObj); // {"x": 6}
例如,用户可以编写如下代码:
mutator
函数的属性:
- 它始终返回
undefined
。 - 它永远不会访问不存在的键。
- 它永远不会删除键(
delete obj.key
)。 - 它永远不会在代理对象上调用方法(
push
、shift
等)。 - 它永远不会将键设置为对象(
proxy.x = {}
)。
关于如何测试解决方案的说明: 解决方案验证器仅分析返回结果与原始 obj
之间的差异。进行完全比较的计算开销太大。此外,对原始对象进行的任何变更都将导致答案错误。
提示:
2 <= JSON.stringify(obj).length <= 4 * 10^5
produce() 的总调用次数 < 10^5
解题思路
可以使用 Proxy
和深拷贝机制,确保原始对象不被改变的同时,允许用户通过代理对象“修改”属性。
深拷贝原始对象:在构造函数中,通过
JSON.parse(JSON.stringify(obj))
进行深拷贝,以确保this.original
是一个全新的对象。使用 Proxy:在
produce
方法中,创建一个Proxy
,用于代理对原始对象的访问,代理允许拦截对对象属性的设置操作。Mutator 函数:调用传入的
mutator
函数,并将代理对象作为参数传递给它。用户可以通过这个代理对象进行修改。返回新对象:在
produce
方法结束时,再进行一次深拷贝以创建一个新的对象并返回。
代码
class ImmutableHelper {
constructor(obj) {
this.original = JSON.parse(JSON.stringify(obj)); // 深拷贝原始对象
}
produce(mutator) {
// 使用 Proxy 来修改对象
const proxy = new Proxy(this.original, {
set: (target, key, value) => {
// 只允许修改代理,不允许直接修改原始对象
if (key in target) {
target[key] = value; // 代理修改
return true;
}
throw new Error(`Cannot set property ${key} on proxy`);
}
});
// 调用 mutator 函数
mutator(proxy);
// 深拷贝代理对象,返回一个新对象,应用修改
return JSON.parse(JSON.stringify(proxy));
}
}
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