#include <iostream>
#include <unordered_set>
#include <vector>
#include <algorithm>
 
using namespace std;
 
int main() {
	vector<pair<int, int> > prerequisites;
	prerequisites.emplace_back(0,1);
	prerequisites.emplace_back(2,0);
 
    int n = 3;
	vector<pair<int, unordered_set<int>>> graph(n); // NO MORE DEFAULT RVALUE
	// We have to find our leaves:
	bool leaf[n];
	for(int i = 0; i < n; i++){
	leaf[i] = true;
	}
 
	for(auto p : prerequisites){
	graph[p.first].first++;
	graph[p.first].second.insert(0); 
	leaf[p.second] = false;
	}
 
	vector<int> leaves;
	for(int i = 0; i < n; i++){
	if(leaf[i])
	    leaves.push_back(i); // This causes a segfault if I don't change it.
	}
}

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