How to optimize the for loop with three levels of nesting?

Question

JavaScript

Hello, I'm new so maybe I don't know the obvious. There are two arrays and a loop:

const arr1 = [
    [432432, 23423, 123123, 54364346],
    [756456, 2423423, 645654, 23423423],
    [12354, 123123, 23423423,1235765]
];

const arr3 = [12354, 5345, 53456346];
const arrResult = [];

for (let i = 0; i < arr1.length; ++i) {
    for (let j = 0; j < arr1[i].length; ++j) {
        for (let k = 0; k < arr3.length; ++k) {
            if (arr1[i][j] === arr3[k]) {
                arrResult.push(arr1[i][j]);
                break;
            }
        }
    }
}

console.log(arrResult);

Since the first array can have quite a lot of values, from 500,000, I would like to know if I can somehow optimize this whole thing? Because now it takes quite a long time. Thanks in advance

Answer 1

If on the forehead:

const arr1 = [
  [ 432432, 23423, 123123, 54364346],
  [ 756456, 2423423, 645654, 23423423],
  [ 12354, 123123, 23423423, 1235765]
]

const arr3 = [ 12354, 5345, 53456346 ]

const arrResult = arr1
  .flat(Infinity)
  .filter(el => arr3.includes(el))

console.log(arrResult)

// Array [ 12354 ]

If you optimize for time, at the expense of memory:

const arr1 = [
  [ 432432, 23423, 123123, 54364346],
  [ 756456, 2423423, 645654, 23423423],
  [ 12354, 123123, 23423423, 1235765]
]

const arr3 = [ 12354, 5345, 53456346 ]

const arr1s = arr1.flat(Infinity)
arr1s.sort((a, b) => a - b)

const arr3s = arr3.slice()
arr3s.sort((a, b) => a - b)

const arrResult = []

for (let i = 0, let j = 0; i < arr1s.length, j < arr3s.length;) {
  if (arr1s[i] === arr3s[j]) {
    arrResult.push(arr1s[i])
    i += 1
  } else if (arr1s[i] < arr3s[j]) {
    i += 1
  } else {
    j += 1
  }
}

console.log(arrResult)

// Array [ 12354 ]

True, in both cases it is necessary to look at the behavior in the presence of duplicates in each of the arrays.