Sample implementation of next permutation

nextperm.cpp

#include <iostream>
#include <algorithm>
using namespace std;

template <typename Container>
bool nextperm(Container &s) {
  using T = Container;
  typename T::iterator first = s.begin();
  typename T::iterator last = s.end() - 1;
  typename T::iterator i = last;

  typename T::iterator ii = i;
  --i;
  while( *ii < *i && i >= first) {
    --i;
    ii = i+1;
  }

  if( ii == first ) {
    std::reverse(ii, s.end());
    return false;
  }

  typename T::iterator j = last;
  while( *j < *i ) {
    --j;
  }

  std::swap(*i, *j);
  std::reverse(ii, s.end());
  return true;
}

int main(int argc, char **argv) {
  string s;
  cin >> s;
  std::sort(s.begin(), s.end());

  // now output the permutations
  cout << "v1:" << endl;
  bool flag = true;
  while( flag ) {
    flag = nextperm(s);
    cout << s << endl;
  }

  cout << "v2:" << endl;
  std::sort(s.begin(), s.end());
  flag = true;
  while( flag ) {
    flag = next_permutation(s.begin(), s.end());
    cout << s << endl;
  }
  return 0;
}