https://www.hackerrank.com/challenges/two-strings
// Complete the twoStrings function below.
string twoStrings(string s1, string s2) {
set<char> s1_chars;
for (auto &c: s1) {
s1_chars.insert(c);
}
for (auto &c: s2) {
if(s1_chars.find(c) != s1_chars.end()) {
return "YES";
}
}
return "NO";
}