Graph Visitor

#include <vector>
#include <functional>
#include <algorithm>

using namespace std;

typedef vector<vector<int>> graph;

void _visit_graph(graph g, int start, vector<int> *visited, function<void(int)> action) {
    if(find(visited->begin(), visited->end(), start) != visited->end()) return;
    action(start);
    visited->push_back(start);
    for_each(g.at(start).begin(), g.at(start).end(),
             [&g, &visited, &action] (int next) { _visit_graph(g, next, visited, action); });
}

void visit_graph(graph g, int start, function<void(int)> action) {
    vector<int> v;
    return _visit_graph(g, start, &v, action);
}