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| #include <bits/stdc++.h>
const int N = 1e5 + 100;
int n, m;
struct Edge{ int ne, ver; } e[N << 1];
int h[N], idx = 0, du[N];
std::priority_queue<int> q;
std::vector<int> ans;
void add(int x, int y){ e[idx] = {h[x], y}, h[x] = idx++; }
void topu()
{
for (int i = 1; i <= n; ++i) if (!du[i]) q.push(i);
while (!q.empty())
{
int x = q.top(); q.pop();
ans.push_back(x);
for (int i = h[x], y; ~i; i = e[i].ne)
{
--du[y = e[i].ver];
if (!du[y]) q.push(y);
}
}
}
int main()
{
int T;
for (scanf("%d", &T); T--; )
{
scanf("%d %d", &n, &m);
memset(h + 1, -1, n << 2), idx = 0;
memset(du + 1, 0, n << 2), ans.clear();
for (int i = 1, u, v; i <= m; ++i)
{
scanf("%d %d", &u, &v);
add(v, u), ++du[u];
}
topu();
bool f = true;
for (int i = 1; i <= n && f; ++i) if (du[i]) f = false;
if (!f) printf("Impossible!");
else
for (int i = ans.size() - 1; ~i; --i) printf("%d ", ans[i]);
puts("");
}
return 0;
}
|