133 lines
2.5 KiB
C++
133 lines
2.5 KiB
C++
/* Problem URL: https://cses.fi/problemset/task/1680 */
|
|
|
|
#include <bits/stdc++.h>
|
|
|
|
using namespace std;
|
|
|
|
#define V vector
|
|
|
|
#define rmin(a, b) a = min(a, b)
|
|
#define rmax(a, b) a = max(a, b)
|
|
|
|
#define rep(i, lim) for (int i = 0; i < (lim); i++)
|
|
#define nrep(i, s, lim) for (int i = s; i < (lim); i++)
|
|
|
|
#define repv(i, v) for (auto &i : (v))
|
|
#define fillv(v) for (auto &itr_ : (v)) { cin >> itr_; }
|
|
#define sortv(v) sort(v.begin(), v.end())
|
|
#define all(v) (v).begin(), (v).end()
|
|
|
|
using vi = vector<int>;
|
|
using vvi = vector<vi>;
|
|
using vvvi = vector<vvi>;
|
|
using vvvvi = vector<vvvi>;
|
|
|
|
using ll = long long;
|
|
|
|
using vl = vector<ll>;
|
|
using vvl = vector<vl>;
|
|
using vvvl = vector<vvl>;
|
|
using vvvvl = vector<vvvl>;
|
|
|
|
template<class v>
|
|
auto operator<<(ostream &os, const vector<v> &vec)->ostream& {
|
|
os << vec[0];
|
|
for (size_t i = 1; i < vec.size(); i++) {
|
|
os << ' ' << vec[i];
|
|
}
|
|
os << '\n';
|
|
return os;
|
|
}
|
|
|
|
template<class v>
|
|
auto operator>>(istream &is, vector<v> &vec)->istream& {
|
|
for (auto &i : vec) {
|
|
is >> i;
|
|
}
|
|
return is;
|
|
}
|
|
|
|
template<class v>
|
|
auto operator<<(ostream &os, const vector<vector<v>> &vec)->ostream& {
|
|
for (auto &i : vec) {
|
|
os << i[0];
|
|
for (size_t j = 1; j < i.size(); j++) {
|
|
os << ' ' << i[j];
|
|
}
|
|
os << '\n';
|
|
}
|
|
return os;
|
|
}
|
|
|
|
template<class v>
|
|
auto operator>>(istream &is, vector<vector<v>> &vec)->istream& {
|
|
for (auto &i : vec) {
|
|
for (auto &j : i) {
|
|
is >> j;
|
|
}
|
|
}
|
|
return is;
|
|
}
|
|
|
|
int main()
|
|
{
|
|
ios::sync_with_stdio(false);
|
|
cin.tie(nullptr);
|
|
|
|
int n, m;
|
|
cin >> n >> m;
|
|
|
|
vvi graph(n);
|
|
|
|
while (m--) {
|
|
int a, b;
|
|
cin >> a >> b;
|
|
|
|
graph[a - 1].push_back(b - 1);
|
|
}
|
|
|
|
vi dp(n, -1);
|
|
|
|
function<int(int)> dfs = [&](int i) {
|
|
if (i == n - 1) {
|
|
dp[i] = 1;
|
|
return dp[i];
|
|
}
|
|
|
|
if (dp[i] != -1) {
|
|
return dp[i];
|
|
}
|
|
|
|
dp[i] = 0;
|
|
|
|
for (auto j : graph[i]) {
|
|
int res = dfs(j);
|
|
if (res > 0) {
|
|
rmax(dp[i], res + 1);
|
|
}
|
|
}
|
|
|
|
return dp[i];
|
|
};
|
|
|
|
if (dfs(0) == 0) {
|
|
cout << "IMPOSSIBLE\n";
|
|
return 0;
|
|
}
|
|
|
|
vi ans = {1};
|
|
|
|
int now = 0;
|
|
while (now != n - 1) {
|
|
for (auto j : graph[now]) {
|
|
if (dp[j] == dp[now] - 1) {
|
|
ans.push_back(j + 1);
|
|
now = j;
|
|
break;
|
|
}
|
|
}
|
|
}
|
|
|
|
cout << ans.size() << '\n' << ans;
|
|
}
|