Nested loop using iterator C++ - c++

Question

Stuck in very interesting problem.
You might have done this before in C/C++
map<string, string> dict;
dsz = dict.size();
vector<string> words;
int sz = words.size();
for(int i = 0; i < sz; ++i)
{
for(int j = i + 1; j < dsz; ++j)
{
}
}
How I will achieve the same thing using iterator.
Please suggest.

Answer 1

Ok.
I figure it out.
more precisely I wanted both i and j in inner loop.
here i did with iterator, sorry I have to move to multimap instead of map due to change in requirement.
vector<string>::iterator vit;
multimap<string, string>::iterator top = dict.begin();
multimap<string, string>::iterator mit;
for(vit = words.begin(); vit != words.end(); ++vit)
{
string s = *vit;
++top;
mit = top;
for(; mit != dict.end(); ++mit)
{
/* compare the value with other val in dictionary, if found, print their keys */
if(dict.find(s)->second == mit->second)
cout << s <<" = "<< mit->first << endl;
}
}
Any other efficient way to do this will be grateful.

Answer 2

Your final intent is not fully clear, because you start the j loop on i+1 (see comments at the end). Until you give clarity on this relationship, I propose you two interim solutions
Approach 1: easy and elegant:
You use the new C++11 range based for(). It makes use of an iterator starting with begin() and going until end(), without you having to bother with this iterator:
for (auto x : words) { // loop on word (size sz)
for (auto y : dict) { // loop on dict (size dsz)
// do something with x and y, for example:
if (x==y.first)
cout << "word " << x << " matches dictionary entry " << y.second << endl;
}
}
Approach 2: traditional use of iterators
You cas also specify explicitely iterators to be used. This is a little bit more wordy as the previous example, but it allows you to choose the best suitable iterator, for example if you want constant iterator like cbegin() instead of begin(), if you want to skip some elements or use an adaptator on the iterator, suc as for example reverse_iterator, etc.:
for (auto itw = words.begin(); itw != words.end(); itw++) {
for (auto itd = dict.begin(); itd != dict.end(); itd++) {
// do simething with *itw and *itd, for example:
if (*itw == itd->first)
cout << "word " << *itw << " matches dictionary entry " << itd->second << endl;
}
}
Remarks:
The starting of intter loop with j=i+1 makes sense only if elements of word vector are related to elements in dict map (ok, they are cerainly words as well), AND if the order of elements you access in the map is related to the order in the vector. As map is ordered according to the key, this would make sense only word would be ordered as well following the same key. Is it the case ?
If you'd still want to skip elements or make calculation based on distance between elements , you'd rather consider the second approach propose above. It makes it easier to use distance(itw, words.begin()) which would be the equivalent of i.
However, it's best to use containters taking advantage of their design. So instead of iterating trough a dictionaly map to find a word entry, it's better to do use the map as follows:
for (auto x : words) { // loop on word (size sz)
if (dict.count(x)) // if x is in dictionary
cout << "word " << x << " matches dictionary entry " << dict[x] << endl;
}