How can I remove duplicate values from a list in c++? [closed]

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I am new to c++ and stuck to a problem. I am using list for storing string values. now i want to remove the duplicate values from that string. Can anyone tell me how do this.

Any sample code will be highly appreciate.

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Use sort followed by unique.

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If the list is sorted, use its unique method.

If the list isn't sorted (and you don't want to sort it):

set<string> found;
for (list<string>::iterator x = the_list.begin(); x != the_list.end();) {
  if (!found.insert(*x).second) {
    x = the_list.erase(x);
  }
  else {
    ++x;
  }
}

To avoid copying the strings into the set:

struct less {
  template<class T>
  bool operator()(T &a, T &b) {
    return std::less<T>()(a, b);
  }
};
struct deref_less {
  template<class T>
  bool operator()(T a, T b) {
    return less()(*a, *b);
  }
};

void remove_unsorted_dupes(list<string> &the_list) {
  set<list<string>::iterator, deref_less> found;
  for (list<string>::iterator x = the_list.begin(); x != the_list.end();) {
    if (!found.insert(x).second) {
      x = the_list.erase(x);
    }
    else {
      ++x;
    }
  }
}

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If you have an std::list you can remove duplicates with:

yourlist.sort();
yourlist.unique();

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Use unique().

But first sort() the list, or unique won't do what you expect.

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Solution 1:

struct already_found
{
  std::set<std::string> & theSet;

  bool operator()(const std::string& s) const
  {
     return !theSet.insert(s).second;
  }
};

std::set<std::string> theSet;
the_list.remove_if( the_list.begin(), the_list.end(), already_found(theSet) );

Solution 2 using shared_ptr

struct already_found
{
  boost::shared_ptr<std::set<std::string> > theSet;
  already_found() : theSet( new boost::shared_ptr<std::set<std::string> > )
  {
  }

  bool operator()(const std::string& s) const
  {
     return !theSet->insert(s).second;
  }
};

the_list.remove_if( the_list.begin(), the_list.end(), already_found(theSet) );

These both have the disadvantage of having to copy all the strings. You can slightly optimise this by storing pointers to the strings and comparing them with a custom compare.