Determines is string s2 is a subsequence of string s1

isSubsequence.cpp

bool isSubsequence(string& s1, string& s2){
    int l1 = s1.length(), l2 = s2.length();
    
    for(int i = 0, j = 0; i < l1; i++){
        if(s1[i] == s2[j] && ++j == l2) return true;
    }
    
    return s2.empty();
}