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input/code.cpp: In function 'void topological_sort()':
input/code.cpp:52:20: warning: statement has no effect [-Wunused-value]
   52 | #define debug(...) 42
      |                    ^~
input/code.cpp:78:5: note: in expansion of macro 'debug'
   78 |     debug(ans);
      |     ^~~~~
input/code.cpp: In function 'bool check()':
input/code.cpp:52:20: warning: statement has no effect [-Wunused-value]
   52 | #define debug(...) 42
      |                    ^~
input/code.cpp:87:5: note: in expansion of macro 'debug'
   87 |     debug(tin);
      |     ^~~~~

#include <bits/stdc++.h>
using namespace std;
#define sz(x) (int)(x).size()
#define all(x) (x).begin(), (x).end()
#define int long long

string to_string(string s) {
    return '"' + s + '"';
}
 
string to_string(const char* s) {
    return to_string((string) s);
}
 
string to_string(bool b) {
    return (b ? "true" : "false");
}
 
template <typename A, typename B>
string to_string(pair<A, B> p) {
    return "(" + to_string(p.first) + ", " + to_string(p.second) + ")";
}
 
template <typename A>
string to_string(A v) {
    bool first = true;
    string res = "{";
    for (const auto &x : v) {
        if (!first) {
            res += ", ";
        }
        first = false;
        res += to_string(x);
    }
    res += "}";
    return res;
}
 
void debug_out() {
    cerr << endl;
}
 
template <typename Head, typename... Tail>
void debug_out(Head H, Tail... T) {
    cerr << " " << to_string(H);
    debug_out(T...);
}
 
#ifdef LOCAL
#define debug(...) cerr << "[" << #__VA_ARGS__ << "]:", debug_out(__VA_ARGS__)
#else
#define debug(...) 42
#endif

int n; // number of vertices
vector<vector<int>> adj; // adjacency list of graph
vector<bool> visited;
vector<int> ans;

void dfs(int v) {
    visited[v] = true;
    for (int u : adj[v]) {
        if (!visited[u])
            dfs(u);
    }
    ans.push_back(v);
}

void topological_sort() {
    visited.assign(n, false);
    ans.clear();
    for (int i = 0; i < n; ++i) {
        if (!visited[i]) {
            dfs(i);
        }
    }
    reverse(ans.begin(), ans.end());
    debug(ans);
}

bool check() {
    vector<int> tin(n);
    for (int i = 0; i < n; i++) {
        tin[ans[i]] = i;
    }

    debug(tin);
    for (int i = 0; i < n; i++) {
        for (int v : adj[i]) {
            if (tin[v] < tin[i]) return false;
        }
    }

    return true;
}

signed main() {
    cin.tie(0)->sync_with_stdio(0);
    
    int m;
    cin >> n >> m;
    adj.resize(n);
    for (int i = 1; i <= m; i++) {
        int u, v;
        cin >> u >> v;
        adj[u - 1].push_back(v - 1);
    }        

    topological_sort();

    if (check()) {
        for (int x : ans) cout << x + 1 << ' ';
    } else {
        cout << "IMPOSSIBLE";
    }
}

Test 1

Verdict: ACCEPTED

Test 2

Verdict: ACCEPTED

Test 3

Verdict: ACCEPTED

Test 4

Verdict: ACCEPTED

Test 5

Verdict: ACCEPTED

Test 6

Verdict: ACCEPTED

Test 7

Verdict: ACCEPTED

Test 8

Verdict: ACCEPTED

Test 9

Verdict: ACCEPTED

Test 10

Verdict: ACCEPTED

Test 11

Verdict: ACCEPTED

Test 12

Verdict: ACCEPTED

Test 13

Verdict: ACCEPTED

Test 14

Verdict: ACCEPTED

Test 15

Verdict: ACCEPTED

Test 16

Verdict: ACCEPTED

Test 17

Verdict: WRONG ANSWER