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#include <iostream>
#include <unordered_map>
using namespace std;
void
dfs (unordered_map<size_t, unordered_map<size_t, int>>& graph,
unordered_map<size_t, int>& been, size_t current)
{
been[current] = 1;
for (auto const& [i, b] : graph[current])
if (b > 0)
if (been[i])
graph[current][i] = graph[i][current] = 0;
else
{
graph[current][i] = graph[i][current] = -1;
dfs (graph, been, i);
}
}
int
main ()
{
size_t n;
unordered_map<size_t, unordered_map<size_t, int>> edges;
cin >> n;
for (size_t i = 0; i < n; ++i)
for (size_t j = 0; j < n; ++j)
{
cin >> edges[i][j];
edges[j][i] = edges[i][j];
}
unordered_map<size_t, unordered_map<size_t, int>> st;
unordered_map<size_t, int> been;
dfs (edges, been, 0);
for (auto const& [i, m] : edges)
for (auto const& [j, b] : m)
if (b && i <= j)
cout << i << " " << j << endl;
}
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