Topological sort using DFS without recursion

Question

I know the common way to do a topological sort is using DFS with recursion. But how would you do it using stack instead of recursion? I need to obtai

Answer 1

Below is my iterative code to topological sorting of DAG.

#include 
#include 
#include 
#include 
#include 
using namespace std;

unordered_map> g;  // this is the simplest graph representation I was able to implement. Map the vertices to their set of children

void addEdge(int x, int y) { // Add edges to the graph
    g[x].insert(y);
}

void topSort() {
    unordered_set visited; // Keep track of visited nodes
    stack mainStack; // The stack that will have the resulting vertices in topologically sorted order

    for(auto it = g.begin(); it != g.end(); it++) {
        if(visited.count(it->first) == 0) { // If the vertex was not already visited do the following
            visited.insert(it->first); // visit the vertex
            stack locStack;
            locStack.push(it->first); // push it to local stack
            while(!locStack.empty()) { // This part is similar to basic DFS algorithm
                int curr = locStack.top();
                bool unVisCh = false; // Keep a boolean to check whether there is any unvisited child
                for(auto it2 = g[curr].begin(); it2 != g[curr].end(); it2++) {
                    int child = *it2;
                    if(visited.count(child) == 0) {
                        unVisCh = true;
                        visited.insert(child);
                        locStack.push(child);
                    }
                }
                if(!unVisCh) { // if there is no unvisited child then we can push the vertex to the resulting stack
                    locStack.pop();
                    mainStack.push(curr);
                }
            }
        }
    }

    while(!mainStack.empty()) {
        cout<

For testing: ideone