---
id: 69bc6cb30c1d112a2e110a05
title: "Challenge 248: Sorted Array Swap"
challengeType: 29
dashedName: challenge-248
---

# --description--

Given an array of integers, return a new array using the following rules:

1. Sort the integers in ascending order
2. Then swap all values whose index is a multiple of 3 with the value before it.

# --hints--

`sort_and_swap([3, 1, 2, 4, 6, 5])` should return `[1, 2, 4, 3, 5, 6]`.

```js
({test: () => { runPython(`
from unittest import TestCase
TestCase().assertEqual(sort_and_swap([3, 1, 2, 4, 6, 5]), [1, 2, 4, 3, 5, 6])`)
}})
```

`sort_and_swap([9, 7, 5, 3, 1, 2, 4, 6, 8])` should return `[1, 2, 4, 3, 5, 7, 6, 8, 9]`.

```js
({test: () => { runPython(`
from unittest import TestCase
TestCase().assertEqual(sort_and_swap([9, 7, 5, 3, 1, 2, 4, 6, 8]), [1, 2, 4, 3, 5, 7, 6, 8, 9])`)
}})
```

`sort_and_swap([1, 2, 3, 4, 5, 6, 7, 8, 9])` should return `[1, 2, 4, 3, 5, 7, 6, 8, 9]`.

```js
({test: () => { runPython(`
from unittest import TestCase
TestCase().assertEqual(sort_and_swap([1, 2, 3, 4, 5, 6, 7, 8, 9]), [1, 2, 4, 3, 5, 7, 6, 8, 9])`)
}})
```

`sort_and_swap([12, 5, 8, 1, 3, 10, 2, 7, 6, 4, 9, 11])` should return `[1, 2, 4, 3, 5, 7, 6, 8, 10, 9, 11, 12]`.

```js
({test: () => { runPython(`
from unittest import TestCase
TestCase().assertEqual(sort_and_swap([12, 5, 8, 1, 3, 10, 2, 7, 6, 4, 9, 11]), [1, 2, 4, 3, 5, 7, 6, 8, 10, 9, 11, 12])`)
}})
```

`sort_and_swap([100, -50, 0, 75, -25, 50, -75, 25])` should return `[-75, -50, 0, -25, 25, 75, 50, 100]`.

```js
({test: () => { runPython(`
from unittest import TestCase
TestCase().assertEqual(sort_and_swap([100, -50, 0, 75, -25, 50, -75, 25]), [-75, -50, 0, -25, 25, 75, 50, 100])`)
}})
```

`sort_and_swap([5, 9, 13, 77, 88, 313, -10, -65, 0, 8, 99, 101, -4, 2])` should return `[-65, -10, 0, -4, 2, 8, 5, 9, 77, 13, 88, 101, 99, 313]`.

```js
({test: () => { runPython(`
from unittest import TestCase
TestCase().assertEqual(sort_and_swap([5, 9, 13, 77, 88, 313, -10, -65, 0, 8, 99, 101, -4, 2]), [-65, -10, 0, -4, 2, 8, 5, 9, 77, 13, 88, 101, 99, 313])`)
}})
```

# --seed--

## --seed-contents--

```py
def sort_and_swap(arr):

    return arr
```

# --solutions--

```py
def sort_and_swap(arr):
    result = sorted(arr)
    for i in range(3, len(result), 3):
        result[i], result[i - 1] = result[i - 1], result[i]
    return result
```