Remove repeating characters from string

Question

I have a string, like e.g. acaddef or bbaaddgg. I have to remove from it, as fast as possible, all repeating characters. So, for example, pooaatat after should look like poat and ggaatpop should look like gatpo. Is there any built-in function or algorithm to do that quickly? I tried to search STL, but without satisfaing result.

Answer 1

Okay, so here are 4 different solutions.

Fixed Array

std::string str = "pooaatat";

// Prints "poat"
short count[256] = {0};
std::copy_if(str.begin(), str.end(), std::ostream_iterator<char>(std::cout),
             [&](unsigned char c) { return count[c]++ == 0; });

Count Algorithm + Iterator

std::string str = "pooaatat";

// Prints "poat"
std::string::iterator iter = str.begin();
std::copy_if(str.begin(), str.end(), std::ostream_iterator<char>(std::cout),
             [&](char c) { return !std::count(str.begin(), iter++, c); });

Unordered Set

std::string str = "pooaatat";

// Prints "poat"
std::unordered_set<char> container;
std::copy_if(str.begin(), str.end(), std::ostream_iterator<char>(std::cout),
             [&](char c) { return container.insert(c).second; });

Unordered Map

std::string str = "pooaatat";

// Prints "poat"
std::unordered_map<char, int> container;
std::copy_if(str.begin(), str.end(), std::ostream_iterator<char>(std::cout),
             [&](char c) { return container[c]++ == 0; });