Suffix Tree of Alignment: An Efficient Index for Similar Data

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We consider an index data structure for similar strings. The generalized suffix tree can be a solution for this. The generalized suffix tree of two strings A and B is a compacted trie representing all suffixes in A and B. It has |A|+|B| leaves and can be constructed in O(|A|+|B|) time. However, if the two strings are similar, the generalized suffix tree is not efficient because it does not exploit the similarity which is usually represented as an alignment of A and B. In this paper we propose a space/time-efficient suffix tree of alignment which wisely exploits the similarity in an alignment. Our suffix tree for an alignment of A and B has |A| + ld + l₁ leaves where ld is the sum of the lengths of all parts of B different from A and l₁ is the sum of the lengths of some common parts of A and B. We did not compromise the pattern search to reduce the space. Our suffix tree can be searched for a pattern P in O(|P|+occ) time where occ is the number of occurrences of P in A and B. We also present an efficient algorithm to construct the suffix tree of alignment. When the suffix tree is constructed from scratch, the algorithm requires O(|A| + ld + l₁ + l₂) time where l₂ is the sum of the lengths of other common substrings of A and B. When the suffix tree of A is already given, it requires O(ld + l₁ + l₂) time.