public String boldWords(String[] words, String S) {

int N = S.length();

boolean[] mask = new boolean[N];

for (int i = 0; i < N; ++i) {

for (String word: words) search: {

for (int k = 0; k < word.length(); ++k) {

if (k + i >= S.length() || S.charAt(k + i) != word.charAt(k)) {

break search;

}

}

for (int j = i; j < i + word.length(); ++j) {

mask[j] = true;

}

}

}

StringBuilder ans = new StringBuilder();

int anchor = 0;

for (int i = 0; i < N; ++i) {

if (mask[i] && (i == 0 || !mask[i - 1])) {

ans.append("<b>");

}

ans.append(S.charAt(i));

if (mask[i] && (i == N - 1 || !mask[i + 1])) {

ans.append("</b>");

}

}

return ans.toString();

}