Language: C++

#include<bits/stdc++.h>
//using namespace std;
#pragma GCC target("avx")
#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")
#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")
#define rep(i,j,n) for(ll i=(ll)(j);i<(ll)(n);i++)
#define REP(i,j,n) for(ll i=(ll)(j);i<=(ll)(n);i++)
#define per(i,j,n) for(ll i=(ll)(j);(ll)(n)<=i;i--)
#define ll long long
#define ALL(a) (a).begin(),(a).end()
#define disup(A,key) distance(A.begin(),upper_bound(ALL(A),(ll)(key)))
#define dislow(A,key) distance(A.begin(),lower_bound(ALL(A),(ll)(key)))
#define pb emplace_back
#define mp std::make_pair
//
#define endl "\n"
//using std::endl;
using std::cin;
using std::cout;
using std::vector;
using std::string;
using std::upper_bound;
using std::lower_bound;
using vi=vector<ll>;
using vii=vector<vi>;
using pii=std::pair<ll,ll>;
//
constexpr ll MOD=1e9+7;
//constexpr ll MOD=998244353;
//constexpr ll MOD=10000000;
//constexpr ll MOD=1e5;
constexpr ll MAX=3e6;
constexpr ll INF=(1ll<<60);
template<class T>
class prique :public std::priority_queue<T, std::vector<T>, std::greater<T>> {};
template<typename T>
struct Segment_tree{
    ll N;
    T mem;
    vector<T> node;
    Segment_tree(vector<T> &X,T m):mem(m){
        ll sz=X.size();
        N=1;
        while(N<sz) N*=2;
        node.resize(2*N-1,mem);
        rep(i,0,sz) node[N-1+i]=X[i];
        per(i,N-2,0){
            node[i]=Compare(node[i*2+1],node[i*2+2]);
        }
    }
    T Compare(T &A,T &B){
        return std::max(A,B);
    }
    void update(ll X,T val){
        X+=N-1;
        node[X]=val;
        while(X>0){
            X=(X-1)/2;
            node[X]=Compare(node[X*2+1],node[X*2+2]);
        }
    }
    T Query(ll a,ll b,ll now,ll l,ll r){ //[a,b),[l,r)
        if(r<0) r=N;
        if(r<=a||b<=l) return mem;
        if(a<=l&&r<=b) return node[now];
        auto vl=Query(a,b,now*2+1,l,(l+r)/2),vr=Query(a,b,now*2+2,(l+r)/2,r);
        return Compare(vl,vr);
    }
};
struct Binary_indexed_tree{
    int N;
    vi bit;
    Binary_indexed_tree(int n):N(n){
        bit.resize(N+1,0);
    }
    void add(int x,int a){
        for(x;x<=N;x+=(x&-x)) bit[x]+=a;
    }
    ll sum(int x){
        ll ret=0;
        for(x;x>0;x-=(x&-x)) ret+=bit[x];
        return ret;
    }
    ll lower_bound(ll X){
        if(sum(N)<X) return -1;
        ll ret=0,memo=1,sum=0;
        while(memo*2<=N) memo*=2;
        while(memo>0){
            if(memo+ret<=N&&sum+bit[memo+ret]<X){
                sum+=bit[memo+ret];
                ret+=memo;
            }
            memo/=2;
        }
        return ret+1;
    }
};
struct Union_Find{
    ll N;
    vi par;
    vi siz;
    Union_Find(int n):N(n){
        par.resize(N);
        siz.resize(N,1);
        rep(i,0,N) par[i]=i;
    }
    ll root(ll X){
        if(par[X]==X) return X;
        return par[X]=root(par[X]);
    }
    bool same(ll X,ll Y){
        return root(X)==root(Y);
    }
    void unite(ll X,ll Y){
        X=root(X);
        Y=root(Y);
        if(X==Y) return;
        par[X]=Y;
        siz[Y]+=siz[X];
        siz[X]=0;
    }
    ll size(ll X){
        return siz[root(X)];
    }
};
long long modpow(long long a, long long n, long long mod) {
    long long res = 1;
    while (n > 0) {
        if (n & 1) res = res * a % mod;
        a = a * a % mod;
        n >>= 1;
    }
    return res;
}
vi fac,finv,inv;
void COMinit() {
    fac.resize(MAX);
    finv.resize(MAX);
    inv.resize(MAX);
    fac[0] = fac[1] = 1;
    finv[0] = finv[1] = 1;
    inv[1] = 1;
    for (int i = 2; i < MAX; i++){
        fac[i] = fac[i - 1] * i % MOD;
        inv[i] = MOD - inv[MOD%i] * (MOD / i) % MOD;
        finv[i] = finv[i - 1] * inv[i] % MOD;
    }
}
ll COM(ll n,ll r){
    if(n<r||n<0||r<0) return 0;
    return fac[n]*finv[r]%MOD*finv[n-r]%MOD;
}
long long modinv(long long a, long long m) {
    long long b = m, u = 1, v = 0;
    while (b) {
        long long t = a / b;
        a -= t * b; std::swap(a, b);
        u -= t * v; std::swap(u, v);
    }
    u %= m; 
    if (u < 0) u += m;
    return u;
}
int main(){
    std::ios::sync_with_stdio(false);
    std::cin.tie(nullptr);
    ll N,M; cin>>N>>M;
    if(M%2){
        cout<<-1<<endl;
        return 0;
    }
    vii edge(N);
    std::set<pii> set;
    vi cnt(N);
    vector<bool> F(N);
    rep(i,0,M){
        ll x,y; cin>>x>>y;
        edge[x-1].pb(y-1);
        edge[y-1].pb(x-1);
        cnt[x-1]++;
        cnt[y-1]++;
    }
    rep(i,0,N){
        set.insert(mp(cnt[i],i));
    }
    while(!set.empty()){
        auto p=*begin(set);
        ll X=p.second;
        set.erase(p);
        ll m=0;
        if(F[X]!=cnt[X]%2){
            ll max=INF;
            rep(i,0,edge[X].size()){
                if(cnt>0) max=std::min(max,cnt[edge[X][i]]);
            }
            for(;m<edge[X].size();m++){
                ll Y=edge[X][m];
                if(cnt[Y]==max){
                    cnt[Y]--;
                    F[Y]=!F[Y];
                    set.erase(mp(cnt[Y]+1,Y));
                    if(cnt[Y])
                    set.insert(mp(cnt[Y],Y));
                    cout<<Y+1<<" "<<X+1<<endl;
                    m++;
                    break;
                }
            }
        }
        cnt[X]=0;
        for(;m<edge[X].size();m++){
            ll Y=edge[X][m];
            if(cnt[Y]>0){
                cnt[Y]--;
                set.erase(mp(cnt[Y]+1,Y));
                if(cnt[Y])
                set.insert(mp(cnt[Y],Y));
                cout<<X+1<<" "<<Y+1<<endl;
            }
        }
    }
}


Compiler output:
a.cc: In function 'int main()':
a.cc:195:23: error: no match for 'operator>' (operand types are 'vi' {aka 'std::vector<long long int>'} and 'int')
  195 |                 if(cnt>0) max=std::min(max,cnt[edge[X][i]]);
      |                    ~~~^~
      |                    |   |
      |                    |   int
      |                    vi {aka std::vector<long long int>}
In file included from /usr/include/c++/14/regex:68,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:181,
                 from a.cc:1:
/usr/include/c++/14/bits/regex.h:1176:5: note: candidate: 'template<class _BiIter> bool std::__cxx11::operator>(const sub_match<_BiIter>&, const sub_match<_BiIter>&)'
 1176 |     operator>(const sub_match<_BiIter>& __lhs, const sub_match<_BiIter>& __rhs)
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1176:5: note:   template argument deduction/substitution failed:
a.cc:195:24: note:   'vi' {aka 'std::vector<long long int>'} is not derived from 'const std::__cxx11::sub_match<_BiIter>'
  195 |                 if(cnt>0) max=std::min(max,cnt[edge[X][i]]);
      |                        ^
/usr/include/c++/14/bits/regex.h:1236:5: note: candidate: 'template<class _Bi_iter, class _Ch_traits, class _Ch_alloc> bool std::__cxx11::operator>(__sub_match_string<_Bi_iter, _Ch_traits, _Ch_alloc>&, const sub_match<_BiIter>&)'
 1236 |     operator>(const __sub_match_string<_Bi_iter, _Ch_traits, _Ch_alloc>& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1236:5: note:   template argument deduction/substitution failed:
a.cc:195:24: note:   'vi' {aka 'std::vector<long long int>'} is not derived from 'std::__cxx11::__sub_match_string<_Bi_iter, _Ch_traits, _Ch_alloc>'
  195 |                 if(cnt>0) max=std::min(max,cnt[edge[X][i]]);
      |                        ^
/usr/include/c++/14/bits/regex.h:1329:5: note: candidate: 'template<class _Bi_iter, class _Ch_traits, class _Ch_alloc> bool std::__cxx11::operator>(const sub_match<_BiIter>&, __sub_match_string<_Bi_iter, _Ch_traits, _Ch_alloc>&)'
 1329 |     operator>(const sub_match<_Bi_iter>& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1329:5: note:   template argument deduction/substitution failed:
a.cc:195:24: note:   'vi' {aka 'std::vector<long long int>'} is not derived from 'const std::__cxx11::sub_match<_BiIter>'
  195 |                 if(cnt>0) max=std::min(max,cnt[edge[X][i]]);
      |                        ^
/usr/include/c++/14/bits/regex.h:1403:5: note: candidate: 'template<class _Bi_iter> bool std::__cxx11::operator>(const typename std::iterator_traits<_Iter>::value_type*, const sub_match<_BiIter>&)'
 1403 |     operator>(typename iterator_traits<_Bi_iter>::value_type const* __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1403:5: note:   template argument deduction/substitution failed:
a.cc:195:24: note:   mismatched types 'const std::__cxx11::sub_match<_BiIter>' and 'int'
  195 |                 if(cnt>0) max=std::min(max,cnt[edge[X][i]]);
      |                        ^
/usr/include/c++/14/bits/regex.h:1497:5: note: candidate: 'template<class _Bi_iter> bool std::__cxx11::operator>(const sub_match<_BiIter>&, const typename std::iterator_traits<_Iter>::value_type*)'
 1497 |     operator>(const sub_match<_Bi_iter>& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1497:5: note:   template argument deduction/substitution failed:
a.cc:195:24: note:   'vi' {aka 'std::vector<long long int>'} is not derived from 'const std::__cxx11::sub_match<_BiIter>'
  195 |                 if(cnt>0) max=std::min(max,cnt[edge[X][i]]);
      |                        ^
/usr/include/c++/14/bits/regex.h:1573:5: note: candidate: 'template<class _Bi_iter> bool std::__cxx11::operator>(const typename std::iterator_traits<_Iter>::value_type&, const sub_match<_BiIter>&)'
 1573 |     operator>(typename iterator_traits<_Bi_iter>::value_type const& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1573:5: note:   template argument deduction/substitution failed:
a.cc:195:24: note:   mismatched types 'const std::__cxx11::sub_match<_BiIter>' and 'int'
  195 |                 if(cnt>0) max=std::min(max,cnt[edge[X][i]]);
      |                        ^
/usr/include/c++/14/bits/regex.h:1673:5: note: candidate: 'template<class _Bi_iter> bool std::__cxx11::operator>(const sub_match<_BiIter>&, const typename std::iterator_traits<_Iter>::value_type&)'
 1673 |     operator>(const sub_match<_Bi_iter>& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1673:5: note:   template argument deduction/substitution failed:
a.cc:195:24: note:   'vi' {aka 'std::vector<long long int>'} is not derived from 'const std::__cxx11::sub_match<_BiIter>'
  195 |                 if(cnt>0) max=std::min(max,cnt[edge[X][i]]);
      |                        ^
In file included from /usr/include/c++/14/bits/stl_algobase.h:64,
                 from /usr/include/c++/14/algorithm:60,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:51:
/usr/include/c++/14/bits/stl_pair.h:1058:5: note: candidate: 'template<class _T1, class _T2> constexpr bool std::operator>(const pair<_T1, _T2>&, const pair<_T1, _T2>&)'
 1058 |     operator>(const pair<_T1, _T2>& __x, const pair<_T1, _T2>& __y)
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_pair.h:1058:5: note:   template argument deduction/substitution failed:
a.cc:195:24: note:   'vi' {aka 'std::vector<long long int>'} is not derived from 'const std::pair<_T1, _T2>'
  195 |                 if(cnt>0) max=std::min(max,cnt[edge[X][i]]);
      |                        ^
In file included from /usr/include/c++/14/bits/stl_algobase.h:67:
/usr/include/c++/14/bits/stl_iterator.h:462:5: note: candidate: 'template<class _Iterator> constexpr bool std::operator>(const reverse_iterator<_Iterator>&, const reverse_iterator<_Iterator>&)'
  462 |     operator>(const reverse_iterator<_Iterator>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:462:5: note:   template argument deduction/substitution failed:
a.cc:195:24: note:   'vi' {aka 'std::vector<long long int>'} is not derived from 'const std::reverse_iterator<_Iterator>'
  195 |                 if(cnt>0) max=std::min(max,cnt[edge[X][i]]);
      |                        ^
/usr/include/c++/14/bits/stl_iterator.h:507:5: note: candidate: 'template<class _IteratorL, class _IteratorR> constexpr bool std::operator>(const reverse_iterator<_Iterator>&, const reverse_iterator<_IteratorR>&)'
  507 |     operator>(const reverse_iterator<_IteratorL>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:507:5: note:   template argument deduction/substitution failed:
a.cc:195:24: note:   'vi' {aka 'std::vector<long long int>'} is not derived from 'const std::reverse_iterator<_Iterator>'
  195 |                 if(cnt>0) max=std::min(max,cnt[edge[X][i]]);
      |                        ^
/usr/include/c++/14/bits/stl_iterator.h:1714:5: note: candidate: 'template<class _IteratorL, class _IteratorR> constexpr bool std::operator>(const move_iterator<_IteratorL>&, const move_iterator<_IteratorR>&)'
 1714 |     operator>(const move_iterator<_IteratorL>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:1714:5: note:   template argument deduction/substitution failed:
a.cc:195:24: note:   'vi' {aka 'std::vector<long long int>'} is not derived from 'const std::move_iterator<_IteratorL>'
  195 |                 if(cnt>0) max=std::min(max,cnt[edge[X][i]]);
      |                        ^
/usr/include/c++/14/bits/stl_iterator.h:1774:5: note: candidate: 'template<class _Iterator> constexpr bool std::operator>(const move_iterator<_IteratorL>&, const move_iterator<_IteratorL>&)'
 1774 |     operator>(const move_iterator<_Iterator>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:1774:5: note:   template argument deduction/substitution failed:
a.cc:195:24: note:   'vi' {aka 'std::vector<long long int>'} is not derived from 'const std::move_iterator<_IteratorL>'
  195 |                 if(cnt>0) max=std::min(max,cnt[edge[X][i]]);
      |                        ^
In file included from /usr/include/c++/14/bits/basic_string.h:47,
                 from /usr/include/c++/14/string:54,
                 from /usr/include/c++/14/bitset:52,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:52:
/usr/include/c++/14/string_view:695:5: note: candidate: 'template<class _CharT, class _Traits> constexpr bool std::operator>(basic_string_view<_CharT, _Traits>, basic_string_view<_CharT, _Traits>)'
  695 |     operator> (basic_string_view<_CharT, _Traits> __x,
      |     ^~~~~~~~
/usr/include/c++/14/string_view:695:5: note:   template argument deduction/substitution failed:
a.cc:195:24: note:   'std::vector<long long int>' is not derived from 'std::basic_string_view<_CharT, _Traits>'
  195 |                 if(cnt>0) max=std::min(max,cnt[edge[X][i]]);
      |                        ^
/usr/include/c++/14/string_view:702:5: note: candidate: 'template<class _CharT, class _Traits> constexpr bool std::operator>(basic_string_view<_CharT, _Traits>, __type_identity_t<basic_string_view<_CharT, _Traits> >)'
  702 |     operator> (basic_string_view<_CharT, _Traits> __x,
      |     ^~~~~~~~
/usr/include/c++/14/string_view:702:5: note:   template argument deduction/substitution failed:
a.cc:195:24: note:   'std::vector<long long int>' is not derived from 'std::basic_string_view<_CharT, _Traits>'
  195 |                 if(cnt>0) max=std::min(max,cnt[edge[X][i]]);
      |                        ^
/usr/include/c++/14/string_view:710:5: note: candidate: 'template<class _CharT, class _Traits> constexpr bool std::operator>(__type_identity_t<basic_string_view<_CharT, _Traits> >, basic_string_view<_CharT, _Traits>)'
  710 |     operator> (__type_identity_t<basic_string_view<_CharT, _Traits>> __x,
      |     ^~~~~~~~
/usr/include/c++/14/string_view:710:5: note:   template argument deduction/substitution failed:
a.cc:195:24: note:   mismatched types 'std::basic_string_view<_CharT, _Traits>' and 'int'
  195 |                 if(cnt>0) max=std::min(max,cnt[edge[X][i]]);
      |                        ^
/usr/include/c++/14/bits/basic_string.h:3915:5: note: can