Finding repeats with fixed gap

We propose an algorithm for finding, within a word, all pairs of occurrences of the same subword within a given distance r. The obtained complexity is O(n log r + S), where S is the size of the output. We also show how the algorithm can be modified in order to find all such pairs of occurrences separated by a given word. The solution uses an algorithm for finding all quasi-squares in two strings, a problem that generalizes the well-known problem of searching for squares.