Raita algorithm

The Raita algorithm is a string searching algorithm published by Timo Raita in 1991 that improves on the Boyer-Moore-Horspool algorithm. Like its parent it preprocesses the pattern to build a bad-character shift table, but it changes the order in which each window of the text is compared with the pattern. It first compares the last character of the pattern with the rightmost character of the window, then the first character with the leftmost, then the middle character with the middle one, and only if all three agree does it compare the remaining characters from the second to the last but one. A mismatch at any stage triggers the bad-character shift computed during preprocessing. Preprocessing takes O(m) time for a pattern of length m, and the search stage takes O(mn) time for a text of length n. The source notes that a similar pre-check appears in modern implementations of std::string::find in the libc++ and libstdc++ libraries.