1. Is_unique.cpp

#include <string>
#include <vector>
#include <iostream>
#include <bitset>
#include <map>
#include <algorithm> // for sort() 

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( string str) {
	
	sort(str.begin(), str.end()); // O(nlogn) sort from <algorithm>

	bool noRepeat = true;
	for ( int i = 0 ; i < str.size() - 1; i++){
		if ( str[i] == str[i+1] ){
			noRepeat = false;
			break;
		}
	}

	return noRepeat;	
}

bool is_unique(string str){
    map<char, int> character_counts;

    for (char c: str){
        for (auto it=character_counts.begin(); it!=character_counts.end(); it++){
            if (c==it->first){
                return false;
            }
        } 
        character_counts[c]=1;
    }
    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_noDS(word) <<endl;
		}
		return 0;
}