Well, I wonder how a compiler finds out dependencies in a header file( one headers needs another and another needs the other and blah blah blah). So let's say -
We have 4 headers named "A", "B", "C" and "D"
--> "A" depends on "B" and "C"
--> "B" depends on "D"
--> "C" doesn't depend on anyone
--> "D" depends on "C"
Here's our problem- How all these headers will be sorted so that before including a header all it's dependencies will be met. And here comes topological sorting. We should sort them like this -
C -- D -- B -- A
So now all dependencies will be met !
Here's how I did that -
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#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
using namespace std;
class StringTopoSort
{
public :
StringTopoSort(vector<string> [],int);
~StringTopoSort();
vector<string> string_topo_sort();
private :
void visit(int index);
int len;
vector<string> * str_lists;
vector<string> unsorted;
vector<string> sorted;
vector<int> * digit_eq;
vector<int> digit_sorted;
vector<bool> is_visited;
};
StringTopoSort :: StringTopoSort(vector<string> * _str_lists,int _len)
{
str_lists = _str_lists;
len = _len;
digit_eq = new vector<int>[len];
for(int i =0; i<len;i++)
{
is_visited.push_back(false);
unsorted.push_back(str_lists[i].at(0));
}
for(int i =0; i<len;i++)
{
for(vector<string>::iterator it = str_lists[i].begin(); it<str_lists[i].end();++it)
{
vector<string> :: iterator index = find(unsorted.begin(),unsorted.end(),*it);
if(index != unsorted.end() )
digit_eq[i].push_back(index-unsorted.begin());
}
}
}
StringTopoSort :: ~StringTopoSort() {}
vector<string> StringTopoSort :: string_topo_sort()
{
for(int i =0;i<len; i++)
{
if(is_visited[i] == false)
visit(i);
}
for(int i = 0; i<digit_sorted.size();i++)
sorted.push_back(unsorted[digit_sorted[i]]);
return sorted;
}
void StringTopoSort :: visit(int index)
{
is_visited[index] = true;
for(vector<int>::iterator i = digit_eq[index].begin(); i<digit_eq[index].end(); i++)
{
if(!is_visited[*i])
visit(*i);
}
digit_sorted.push_back(index);
}
int main(int argc, char ** argv)
{
vector<string> headers[] = {{"A","B","C"},{"B","D"},{"C"},{"D","C"}};
StringTopoSort sorter(headers,4);
vector<string> sorted = sorter.string_topo_sort();
for(int i =0; i<sorted.size(); i++)
cout << sorted[i] << " -- ";
cout << endl;
return 0;
}
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And here we go -
The StringTopoSort doesn't need c++11, but the declaration of headers here needs
this. So you have to compile it by -
g++ main.cpp -std=c++1
