How to represent adjacency list using vector in c++

Hi
I have the following adjacenecy matrix
0 1 1 0
1 0 0 0
1 3 1 1
1 0 0 1

I need  to implement adjacenecy list for this matrix and then go ahead with Dijkstra's algorith to find the shortest path. I dont know how to create a 1D or 2D vector to reprsent the adj list structure.
Pleas help me on this regard.
BeebutterAsked:
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itsmeandnobodyelseConnect With a Mentor Commented:
>>>> I dont know how to create a 1D or 2D vector to reprsent the adj list structure.

For a fixed sized 4x4 matrix you would use normal C 2-D arrays:

    int adm[4][4] = {
                                  { 0, 1, 1, 0, },
                                  { 1, 0, 0, 0, },
                                  { 1, 3, 1, 1, },
                                  { 1, 0, 0, 1, },
                             };

you then may have loops like

    for (int r = 0; r < 4; ++r)
    {
          for (int c = 0; c < 4; ++c)
          {
                 int cell = adm[r][c];
                 ...
           }
     }

If the matrix may have arbitrary size or if you need to make calulations, I would suggest to define a own class

class ADM
{
      int** matrix;
      int     maxrow;
      int     maxcol;
public:
      ADM(int mr, int mc) : matrix(NULL), maxrow(mr), maxcol(mc)
      {
           if (mr <= 0 ||mc <= 0)
           {  maxrow = maxcol = 0; return; }
           matrix = new int*[maxrow];
           for (int r = 0; r < maxcol; ++r)
                matrix[r] = new int[maxcol];
           memset(matrix, 0, maxrow*maxcol*sizeof(int);
      }
      ~ADM()
     {
           for (int r = 0; r < maxcol; ++r)
                delete [] matrix[r];
           delete [] matrix;
      }
      bool init(int* m, int mr, int mc)
      {
           if (mr != maxrow || mc != maxcol) return false;
           for (int r = 0; r < mr; ++r)
          {
             for (int c = 0; c < mc; ++c)
             {
                matrix[r][c] = m[r*mc+c];
             }
           }
      }
      int& operator()(int r, int c)
      {
          static int err = -1;
          if (r >= 0 && r < maxrow && c >= 0 && c < maxcol)
             return matrix[r][c];
         return err;  // return reference to error variable
      }
      // more functions and operators for matrix manipulation and calculation
};

You could use the above like

    static int adminit[4][4] = {
                                  { 0, 1, 1, 0, },
                                  { 1, 0, 0, 0, },
                                  { 1, 3, 1, 1, },
                                  { 1, 0, 0, 1, },
                             };
      ADM adm(4, 4);
      adm.init(&adminit[0][0], 4, 4);

      int cell = adm(2, 1);  // get the 3 of above matrix



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BeebutterAuthor Commented:
Is anybody looking in to this problem?
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BeebutterAuthor Commented:
Well, Thank you for your detailed response. But still it doesn't meet up to be a solution to my problem.
I have to get an adjacency list structure using vector or linked lists. The above said solution deals with adjacenecy matrix only. A adj list structure would like this for that above mentioned ADj matrix.

vertex 0 -> 1, 2
vertex 1 -> 0
vertex 2 -> 0, 1, 2, 3
vertex 3 -> 0, 4

Adj list would provide me details of all outgoing nodes from each vertex and the cost associated with it. Using this I have to implement Dijkstra's algorithm.

Is there any way of doing this, using a vector or linked list or anything else ?????
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itsmeandnobodyelseCommented:
If you would define the ADM

class ADM
{
    vector<list<int> > adm;
    ...

};

you exactly meet the requirements (though it is not much won by that ...).
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BeebutterAuthor Commented:
Ok I will try doing that way
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BeebutterAuthor Commented:
I tried doing like this

vector<list<int> > adjacencyList;
list<int> inList;
for (int i = 0; i < 4; i++) {
inList.clear();
offset = 0;
getline(inputFile, s);
for (int j = 0; j < 4; j++) {
sscanf(s.c_str() + offset, "%d ", &cost);
offset = s.find_first_of(" ", offset + 1);
inList.push_back(cost);
}

for (int i = 0; i < 4; i++) {
for (int j = 0; j < 4; j++)
cout << adjacencyList[i][j] << " "; // not working
cout << "\n";
}
adjacencyList.push_back(inList);
}


I dont know how to print the contents in the list in the vector.
Can you please tell me where i am going wrong and how to solve?
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BeebutterAuthor Commented:
sorry i missed two lines over there

I tried doing like this

vector > adjacencyList;
list inList;
for (int i = 0; i < 4; i++) {
inList.clear();
offset = 0;
getline(inputFile, s);
for (int j = 0; j < 4; j++) {
sscanf(s.c_str() + offset, "%d ", &cost);
offset = s.find_first_of(" ", offset + 1);
inList.push_back(cost);
}
adjacencyList.push_back(inList);
}
for (int i = 0; i < 4; i++) {
for (int j = 0; j < 4; j++)
cout << adjacencyList[i][j] << " "; // not working
cout << "\n";
}
adjacencyList.push_back(inList);
}



I dont know how to print the contents in the list in the vector.
Can you please tell me where i am going wrong and how to solve?
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itsmeandnobodyelseCommented:
First, I strongly would suggest to make a proper indent.

vector<list<int> > adjacencyList;
list<int> inList;
for (int i = 0; i < 4; i++)
{
    inList.clear();
    offset = 0;
    getline(inputFile, s);
    for (int j = 0; j < 4; j++)
    {
        sscanf(s.c_str() + offset, "%d ", &cost);
        offset = s.find_first_of(" ", offset + 1);
        inList.push_back(cost);
    }
    adjacencyList.push_back(inList);
}
for (int i = 0; i < 4; i++)
{
    for (int j = 0; j < 4; j++)
        cout << adjacencyList[i][j] << " "; // not working
    cout << "\n";
}
adjacencyList.push_back(inList);
}

Then, you probably would have seen that there are two lines more in the post than in your source. If you were using Visual Studio simply select all source lines and press ALT+F8 to make the indentation.

Second, do not mix C and C++ if not necessary. Here it is the use of sscanf, which can be made better and safer in C++ using stringstreams.

  istringstream iss(s);
  while (iss >> cost)
      inList.push_back(cost);

>>>> cout << adjacencyList[i][j]
That doesn't compile cause std::list has no operator[] . You either need to replace the list<int> by vector<int> or - better- use std::list<int> iterator for iterating rather than expecting 4 values (what would explode for shorter lists as in your sample).

   vector<list<int> >::iterator itr;
   list<int>::iterator itl;
   for (itr=adjacencyList.begin();  itr!=adjacencyList.end(); ++itr)
       for (itl= itr->begin(); itl != itr->end(); ++itl)
             cout << *itl << " "; //  working


 


 
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