Determining if a particular string has all unique characters (in C++)

<predata-previewers=””>#include <string>
#include <vector>
#include <iostream>
#include <bitset>
using namespace std;
bool isUniqueChars(const string &str){
if (str.length() > 128){
return false;
}
vector<bool> char_set(128);
for (int i = 0; i < str.length(); i++){
int val = str[i];
if (char_set[val]){
return false;
}
char_set[val] = true;
}
return true;
}
bool isUniqueChars_bitvector(const string &str) {
//Reduce space usage by a factor of 8 using bitvector.
//Each boolean otherwise occupies a size of 8 bits.
bitset<256> bits(0);
for(int i = 0; i < str.length(); i++) {
int val = str[i];
if(bits.test(val) > 0) {
return false;
}
bits.set(val);
}
return true;
}
bool isUniqueChars_noDS(const string &str) {
for(int i = 0; i < str.length()-1; i++) {
for(int j = i+1; j < str.length(); j++) {
if(str[i] == str[j]) {
return false;
}
}
}
return true;
}
int main(){
vector<string> words = {"abcde", "hello", "apple", "kite", "padle"};
for (auto word : words)
{
cout << word << string(": ") << boolalpha << isUniqueChars(word) <<endl;
}
cout <<endl << "Using bit vector" <<endl;
for (auto word : words)
{
cout << word << string(": ") << boolalpha << isUniqueChars_bitvector(word) <<endl;
}
cout <<endl << "Using no Data Structures" <<endl;
for (auto word : words)
{
cout << word << string(": ") << boolalpha << isUniqueChars_bitvector(word) <<endl;
}
return 0;
}