Knuth-Morris-Pratt string search

func kmp_search (String S, String W) {

    S.graphemes!
    W.graphemes!

    func kmp_table {
        var (pos, cnd, *T) = (1, 0, -1)
        for (nil; pos < W.len; (++pos; ++cnd)) {
            if (W[pos] == W[cnd]) {
                T[pos] = T[cnd]
            }
            else {
                T[pos] = cnd
                while ((cnd >= 0) && (W[pos] != W[cnd])) {
                    cnd = T[cnd]
                }
            }
        }
        T[pos] = cnd
        return T
    }

    var (k, T, *I) = (0, kmp_table())

    for (var j = 0; j < S.len; nil) {
        if (W[k] == S[j]) {
            ++j
            ++k
            if (k == W.len) {
                I << (j - k)
                k = T[k]
            }
        }
        elsif ((k = T[k]) < 0) {
            ++j
            ++k
        }
    }

    return I
}

var texts = [
    "GCTAGCTCTACGAGTCTA",
    "GGCTATAATGCGTA",
    "there would have been a time for such a word",
    "needle need noodle needle",
    "BharôtভাৰতBharôtভারতIndiaBhāratભારતBhāratभारतBhārataಭಾರತBhāratभारतBhārat"+
    "amഭാരതംBhāratभारतBhāratभारतBharôtôଭାରତBhāratਭਾਰਤBhāratamभारतम्Bārataபாரத"+
    "ம்BhāratamഭാരതംBhāratadēsamభారతదేశం",
    "InhisbookseriesTheArtofComputerProgrammingpublishedbyAddisonWesleyDKnu"+
    "thusesanimaginarycomputertheMIXanditsassociatedmachinecodeandassemblyl"+
    "anguagestoillustratetheconceptsandalgorithmsastheyarepresented",
    "Nearby farms grew a half acre of alfalfa on the dairy's behalf, with ba"+
    "les of all that alfalfa exchanged for milk.",
]

var pats = ["TCTA", "TAATAAA", "word", "needle", "ഭാരതം", "put", "and", "alfalfa"]

texts.each_kv {|k,v| say "text#{k} = #{v}" }; say ''

pats.each_kv {|k,v|
    var j = (k < 6 ? k : k-1)
    say ("Found '#{v}' in 'text#{j}' at indices ", kmp_search(texts[j], v))
}

Output:

text0 = GCTAGCTCTACGAGTCTA
text1 = GGCTATAATGCGTA
text2 = there would have been a time for such a word
text3 = needle need noodle needle
text4 = BharôtভাৰতBharôtভারতIndiaBhāratભારતBhāratभारतBhārataಭಾರತBhāratभारतBhāratamഭാരതംBhāratभारतBhāratभारतBharôtôଭାରତBhāratਭਾਰਤBhāratamभारतम्Bārataபாரதம்BhāratamഭാരതംBhāratadēsamభారతదేశం
text5 = InhisbookseriesTheArtofComputerProgrammingpublishedbyAddisonWesleyDKnuthusesanimaginarycomputertheMIXanditsassociatedmachinecodeandassemblylanguagestoillustratetheconceptsandalgorithmsastheyarepresented
text6 = Nearby farms grew a half acre of alfalfa on the dairy's behalf, with bales of all that alfalfa exchanged for milk.

Found 'TCTA' in 'text0' at indices [6, 14]
Found 'TAATAAA' in 'text1' at indices []
Found 'word' in 'text2' at indices [40]
Found 'needle' in 'text3' at indices [0, 19]
Found 'ഭാരതം' in 'text4' at indices [68, 138]
Found 'put' in 'text5' at indices [26, 90]
Found 'and' in 'text5' at indices [101, 128, 171]
Found 'alfalfa' in 'text6' at indices [33, 87]