#include <bits/stdc++.h>
using namespace std;
// //------------------------------------------------------------------------
// //for POLICY BASED DATA STRUCTURE
// #include <ext/pb_ds/assoc_container.hpp>
// #include <ext/pb_ds/tree_policy.hpp>
// using namespace __gnu_pbds;
// //stores unique integers in increasing order
// typedef tree<int, null_type, less<int>, rb_tree_tag, tree_order_statistics_node_update> ordered_set;
// //stores unique integers in descreasing order
// typedef tree<int, null_type, greater<int>, rb_tree_tag, tree_order_statistics_node_update> ordered_set;
// //store integers in increasing order(can store duplicate integers also like multiset)
// typedef tree<int, null_type, less_equal<int>, rb_tree_tag, tree_order_statistics_node_update> ordered_set1;
// //store integers in decreasing order(can store duplicate integers also like multiset)
// typedef tree<int, null_type, greater_equal<int>, rb_tree_tag, tree_order_statistics_node_update> ordered_set2;
// // Declaring ordered_set for pair<int,int>
// typedef tree<pair<int,int>, null_type, less<pair<int,int>>, rb_tree_tag,tree_order_statistics_node_update> ordered_set_pair;
// //------------------------------------------------------------------------
#define forn(i, n) for (int i = 0; i < n; i++)
#define um unordered_map
#define us unordered_set
#define sz(v) (int)v.size()
#define all(x) x.begin(), x.end()
#define pb push_back
#define rep(i, a, b) for (int i = a; i <=b; ++i)
#define pii pair<int, int>
#define fi first
#define se second
typedef long long ll;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<pii> vii;
const ll md = 1e9 + 7;
const ll inf = LLONG_MAX;
// Graph Grid //
int dirs[] = {0, 1, 0, -1, 0};
int dirx[8] = {-1, 0, 0, 1, -1, -1, 1, 1};
int diry[8] = {0, 1, -1, 0, -1, 1, -1, 1};
// print matrix
void print(vector<vector<int>> &v)
{
for (auto &c : v)
{
for (auto i : c)
cout << i << " ";
cout << "\n";
}
}
// print 1-D vector
void pri(vi &v)
{
for (int i : v)
cout << i << ' ';
cout << '\n';
}
// pow(x,n), INT_MIN <=n<= INT_MAX, 'n' is an int and 'x' is a double
double myPow(double x, int n)
{
double ans = 1.0;
long long nn = n;
if (nn < 0)
nn *= (-1);
while (nn)
{
if (nn % 2) // if n is odd
{
ans *= x;
nn -= 1;
}
else // n is even
{
x *= x;
nn /= 2;
}
}
if (n < 0) // power is negative
ans = 1 / ans;
return ans;
}
// pow(x,n)%mod
int binaryExponentiation(int x, int n, int mod)
{
int res = 1;
while (n > 0)
{
if (n & 1)
res = (res* 1LL * x) % mod;
x = (x * 1LL * x) % mod;
n >>= 1;
}
return res;
}
// bool sieve[1e8];
// void createSieve(int N)
// {
// for(int i=0;i<1e8;i++)
// sieve[i]=true; // initially assuming all numbers are prime
// sieve[1]=false;
// for(int i=2;i*i<=N;i++)
// if(sieve[i])
// for(int j=i*i;j<=N;j+=i)
// sieve[j]=false;
// }
vector<bool>visited(1e5+1,false);
vi order(1e5+1,0);
vi hh;
bool solve(int src,vi adj[])
{
visited[src]=true;
order[src]=1;
hh.pb(src);
for(auto x:adj[src])
{
if(!visited[x])
{
bool conf=solve(x,adj);
if(conf) return true;
}
else if(order[x]) return true;
}
order[src]=0;
hh.pop_back();
return false;
}
bool isCycle(int V,vi adj[])
{
for(int i=1;i<=V;i++)
{
if(!visited[i])
{
bool c=solve(i,adj);
if(c) return true;
}
}
return false;
}
void solve()
{
int n,m;
cin>>n>>m;
vi adj[n+1];
forn(i,m)
{
int u,v;
cin>>u>>v;
adj[u].pb(v);
}
bool res=isCycle(n,adj);
if(!res)
{
cout<<"IMPOSSIBLE";
return;
}
int cnt=0;
for(auto i:order)
if(i) cnt++;
cout<<cnt<<'\n';
// for(int i=1;i<=n;i++)
// if(order[i]) cout<<i<<' ';
pri(hh);
}
int main()
{
ios_base::sync_with_stdio(false);
cin.tie(NULL);
// int t;
// cin >> t;
// while (t--)
solve();
return 0;
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C++ is a widely used middle-level programming language.
When ever you want to perform a set of operations based on a condition If-Else is used.
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You can also use if-else for nested Ifs and If-Else-If ladder when multiple conditions are to be performed on a single variable.
Switch is an alternative to If-Else-If ladder.
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For loop is used to iterate a set of statements based on a condition.
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While is also used to iterate a set of statements based on a condition. Usually while is preferred when number of iterations are not known in advance.
while (condition) {
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Do-while is also used to iterate a set of statements based on a condition. It is mostly used when you need to execute the statements atleast once.
do {
// code
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return_type function_name(parameters);
function_name (parameters)
return_type function_name(parameters) {
// code
}