Good evening! Here's our prompt for today.

This problem is named the "Dutch national flag problem" because the flag of the Netherlands is comprised of the colors red, white, and blue in separate parts. Although we won't be using colors, the premise of the challenge is to develop a sorting algorithm that performs some form of separations of three kinds of elements.

To simplify things, we'll use 0s, 1s, and 2s.

Given an array consisting of only 0s, 1s, and 2s, sort the elements in linear time and constant space.

1const arr = [2, 0, 1, 0, 2]
2dutchNatFlag(arr)
3// [0, 0, 1, 2, 2]

Constraints

• Length of the array <= 100000

Try to solve this here or in Interactive Mode.

How do I practice this challenge?

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    'PASSED: assert.deepEqual(dutchNatFlag([2, 0, 0, 1, 1, 0, 2, 2]), [0, 0, 0, 1, 1, 2, 2, 2]);'

var assert = require('assert');

​

function swap(arr, first, second) {}

​

function dutchNatFlag(arr) {

  // Fill in this method

  return arr;

}

​

dutchNatFlag([2, 2, 2, 0, 0, 0, 1, 1]);

​

try {

  assert.deepEqual(dutchNatFlag([2, 0, 1, 0, 2]), [0, 0, 1, 2, 2]);

​

  console.log(

    'PASSED: assert.deepEqual(dutchNatFlag([2, 0, 1, 0, 2]), [0, 0, 1, 2, 2]);'

  );

} catch (err) {

  console.log(err);

}

​

try {

  assert.deepEqual(dutchNatFlag([0, 1, 2]), [0, 1, 2]);

​

  console.log(

    'PASSED: ' + 'assert.deepEqual(dutchNatFlag([0, 1, 2]), [0, 1, 2]);'

  );

} catch (err) {

  console.log(err);

Here's our guided, illustrated walk-through.

How do I use this guide?