检查数组是否包含2个不同值的最快方法？

Question

Consider the following arrays:

['a', 'b', 'a'] //method should return true
['a', 'b', 'c'] //method should return true
['a', 'c', 'c'] //method should return false

I want to write a method that most efficiently checks to see if both 'a' and 'b' exist in the array. I know I can do this in a simple for loop

let a_counter = 0;
let b_counter = 0;
for (let i = 0; i < array.length; i++) {
    if (array[i] === 'a') {
        a_counter++;
    }
    if (array[i] === 'b') {
        b_counter++;
    }
}
return (a_counter > 0 && b_counter > 0);

But this isn't very short. I can do indexOf but that will loop through twice. I have also considered using a set as below:

const letter_set = new Set(array)
return (letter_set.has('a') && letter_set.has('b')) 

But I am pretty unfamiliar with sets and don't know if this solution could potentially be more expensive than just looping. I know that has() operations should be faster than array iterations but constructing the set probably takes at least O(N) time (I'm assuming).

Is there a clean and efficient way to find multiple elements in an array? ES6 answers welcome

Answer 1

You could use just the Set and check if the wanted items are in the items array.

 const check = (items, wanted) => wanted.every(Set.prototype.has, new Set(items)); console.log(check(['a', 'b', 'a'], ['a', 'b'])); // true console.log(check(['a', 'b', 'c'], ['a', 'b'])); // true console.log(check(['a', 'c', 'c'], ['a', 'b'])); // false 

Answer 2

You can use every and includes to do this check.

So we are saying every item must be included in the array.

 function contains(arr, ...items) { return items.every(i => arr.includes(i)) } console.log(contains(['a', 'b', 'a'], 'a', 'b')) console.log(contains(['a', 'c', 'c'], 'a', 'b')) console.log(contains(['a', 'b', 'c'], 'a', 'b', 'c')) console.log(contains(['a', 'b', 'c', 'd'], 'a', 'b', 'c', 'd', 'e')) 

Answer 3

array.includes('a') && array.includes('b')

即使有多个元素， includes似乎也是检查特定元素的一种便捷方法。

Answer 4

Not as compact as the other examples, but it does do the job in single run.

 const arr1 = ['a', 'b', 'a']; //method should return true const arr2 = ['a', 'c', 'c']; //method should return false const arr3 = ['a', 'b', 'c']; //method should return true const reducer = ({ a, b }, char) => ({ a: a || char === 'a', b: b || char === 'b' }); const includesAnB = arr => { const { a, b } = arr.reduce(reducer, {}); return a && b; } console.log(includesAnB(arr1)); console.log(includesAnB(arr2)); console.log(includesAnB(arr3));