Optimal Parallel Algorithms for String Matching

Let WRAM [PRAM]be a parallel computer with p processors (RAMs) which share a common memory and are allowed simultaneous reads and writes [only simultaneous reads]. The only type of simultaneous writes allowed is a simultaneous AND: a subset of the processors may write 0 simultaneously into the same memory cell. Let t be the time bound of the computer. We design below families of parallel algorithms that solve the string matching problem with inputs of size n ( n is the sum of lengths of the pattern and the text) and have the following performance in terms of p, t and n : (1) For WRAM: pt = O ( n ) for p ⩽ n /log n (i.e., t ⩾ log n ). † (2) for PRAM: pt = O ( n ) for p ⩽ n /log 2 n (i.e., t ⩾ log 2 n ). (3) For WRAM: t = constant for p = n 1 + e and any e > 0. (4) For WRAM: t = O (log n /log log n ) for p = n . Similar families are also obtained for the problem of finding all initial palindromes of a given string.