# Frequent Words Problem solved by 1518

Sept. 27, 2013, 3:39 p.m. by Rosalind Team

This is the first problem in a collection of "code challenges" to accompany Bioinformatics Algorithms: An Active-Learning Approach by Phillip Compeau & Pavel Pevzner.

A k-mer is a string of length k. We define Count(Text, Pattern) as the number of times that a k-mer Pattern appears as a substring of Text. For example,

$\textit{Count}(\text{ACA}\color{green}\textbf{ACTAT}\color{black}\text{GCAT}\color{green}\textbf{ACTAT}\color{black}\text{CGGGA}\color{green}\textbf{ACTAT}\color{black}\text{CCT}, {\color{green}\textbf{ACTAT}}) = 3$.

We note that Count($\text{CG}\color{green}\textbf{ATATA}\color{black}\text{TCC}\color{green}\textbf{ATA}\color{black}\text{G}$, $\color{green}\textbf{ATA}$) is equal to 3 (not 2) since we should account for overlapping occurrences of Pattern in Text.

We say that Pattern is a most frequent k-mer in Text if it maximizes Count(Text, Pattern) among all k-mers. For example, "ACTAT" is a most frequent 5-mer in "ACAACTATGCATCACTATCGGGAACTATCCT", and "ATA" is a most frequent 3-mer of "CGATATATCCATAG".

## Frequent Words Problem

Find the most frequent k-mers in a string.

Given: A DNA string Text and an integer k.

Return: All most frequent k-mers in Text (in any order).

## Sample Dataset

ACGTTGCATGTCGCATGATGCATGAGAGCT
4


## Sample Output

CATG GCAT