Most common substring of length X

Question

I have a string s and I want to search for the substring of length X that occurs most often in s. Overlapping substrings are allowed.

For example, if s=\"aoaoa\" and X=3

Answer 1

Naive solution in Python

from collections import defaultdict
from operator    import itemgetter

def naive(s, X):
    freq = defaultdict(int)
    for i in range(len(s) - X + 1):
        freq[s[i:i+X]] += 1
    return max(freq.iteritems(), key=itemgetter(1))

print naive("aoaoa", 3)
# -> ('aoa', 2)

In plain English

1. Create mapping: substring of length X -> how many times it occurs in the s string

   for i in range(len(s) - X + 1):
       freq[s[i:i+X]] += 1
   

2. Find a pair in the mapping with the largest second item (frequency)

   max(freq.iteritems(), key=itemgetter(1))