static int findLength(const string& str) {
int windowStart = 0;
int maxLength = 0;
set<char> entries;
int windowEnd = 0;
while( windowEnd < str.length()) {
if(entries.find(str[windowEnd]) != entries.end()) {
entries.erase(str[windowStart]);
windowStart++;
} else {
entries.insert(str[windowEnd]);
maxLength = max(maxLength, int(entries.size()));
windowEnd++;
}
}
return maxLength;
}