What is a need of defining indegree vector in private for finding All Topological Sorts of DAG? - oop

Question

What is the importance of defining indegree vector in the private of a class? It could have been defined in alltopologicalSort() function.
class Graph
{
int V; // No. of vertices
// Pointer to an array containing adjacency list
list<int> *adj;
// Vector to store indegree of vertices
vector<int> indegree;
// A function used by alltopologicalSort
void alltopologicalSortUtil(vector<int>& res,
bool visited[]);
public:
Graph(int V); // Constructor
// function to add an edge to graph
void addEdge(int v, int w);
// Prints all Topological Sorts
void alltopologicalSort();
};
And how it is functioning in below addedge function
void Graph::addEdge(int v, int w)
{
adj[v].push_back(w); // Add w to v's list.
// increasing inner degree of w by 1
indegree[w]++;
}
Use of indegree, please explain here the role of addEdge function in decrementing indegree
void Graph::alltopologicalSortUtil(vector<int>& res,
bool visited[])
{
// To indicate whether all topological are found
// or not
bool flag = false;
for (int i = 0; i < V; i++)
{
// If indegree is 0 and not yet visited then
// only choose that vertex
if (indegree[i] == 0 && !visited[i])
{
// reducing indegree of adjacent vertices
list<int>:: iterator j;
for (j = adj[i].begin(); j != adj[i].end(); j++)
indegree[*j]--;
// including in result
res.push_back(i);
visited[i] = true;
alltopologicalSortUtil(res, visited);
// resetting visited, res and indegree for
// backtracking
visited[i] = false;
res.erase(res.end() - 1);
for (j = adj[i].begin(); j != adj[i].end(); j++)
indegree[*j]++;
flag = true;
}
}
}
This is the link to complete code of finding All Topological Sorts of Directed Acyclic Graph
https://www.geeksforgeeks.org/all-topological-sorts-of-a-directed-acyclic-graph/

Answer 1

I have got my answer from above discussion with Gupta and kaya3
Indegree could have been defined in some function and then passed to alltopologicalSort() function as a reference. But then defining it in class makes it easier to deal with.
And Data members of a class are always kept private because of encapsulation rules