Update READMEs.

Author: trekhleb

README.md

@@ -236,7 +236,7 @@ Below is the list of some of the most used Big O notations and their performance
 | **Selection sort**    | `n^2`       | `n^2`       | `n^2`           | `1`         | No        |           |
 | **Heap sort**         | `n log(n)`  | `n log(n)`  | `n log(n)`      | `1`         | No        |           |
 | **Merge sort**        | `n log(n)`  | `n log(n)`  | `n log(n)`      | `n`         | Yes       |           |
-| **Quick sort**        | `n log(n)`  | `n log(n)`  | `n^2`           | `log(n)`    | No        |           |
-| **Shell sort**        | `n log(n)`  | depends on gap sequence   | `n (log(n))^2`  | `1`         | No        |           |
+| **Quick sort**        | `n log(n)`  | `n log(n)`  | `n`<sup>`2`</sup>           | `log(n)`    | No        |           |
+| **Shell sort**        | `n log(n)`  | depends on gap sequence   | `n (log(n))`<sup>`2`</sup>  | `1`         | No        |           |
 | **Counting sort**     | `n + r`     | `n + r`     | `n + r`         | `n + r`     | Yes       | `r` - biggest number in array |
 | **Radix sort**        | `n * k`     | `n * k`     | `n * k`         | `n + k`     | Yes       | `k` - length of longest key |