KMP模版

int kmp(const string& text, const string& pattern) {
    int n = text.size(), m = pattern.size();
    if (m == 0) {
        return 0;
    }
    vector<int> next(m);
    for (int i = 1, j = 0; i < m; i++) {
        while (j > 0 && pattern[i] != pattern[j]) {
            j = next[j - 1];
        }
        if (pattern[i] == pattern[j]) {
            j++;
        }
        next[i] = j;
    }
    for (int i = 0, j = 0; i < n; i++) {
        while (j > 0 && text[i] != pattern[j]) {
            j = next[j - 1];
        }
        if (text[i] == pattern[j]) {
            j++;
        }
        if (j == m) {
            return i - m + 1;
        }
    }
    return -1;
}

C++