Submission #653094

#	Time	Username	Problem	Language	Result	Execution time	Memory
653094		MilosMilutinovic	Parking (CEOI22_parking)	C++14	10 / 100	168 ms	19176 KiB

Main

#include <bits/stdc++.h>
using namespace std;
#define rep(i,a,n) for (int i=a;i<n;i++)
#define per(i,a,n) for (int i=n-1;i>=a;i--)
#define pb push_back
#define eb emplace_back
#define mp make_pair
#define all(x) (x).begin(),(x).end()
#define fi first
#define se second
#define SZ(x) ((int)(x).size())
typedef vector<int> VI;
typedef basic_string<int> BI;
typedef long long ll;
typedef pair<int,int> PII;
typedef double db;
mt19937 mrand(random_device{}());
const ll mod=998244353;
int rnd(int x) { return mrand() % x;}
ll powmod(ll a,ll b) {ll res=1;a%=mod; assert(b>=0); for(;b;b>>=1){if(b&1)res=res*a%mod;a=a*a%mod;}return res;}
ll gcd(ll a,ll b) { return b?gcd(b,a%b):a;}
// head

const int N=200200;
int n,m,a[N],b[N],bb[N],cnt[N][2];
vector<PII> ps[N];

void add(int x,int i,int p) {
    if (!x) return;
    cnt[x][p]++;
    ps[x].pb(mp(i,p));
}

set<int> tp,tp00,tp01;
void ins(int x) {
//    printf("ins %d\n",x);
    bb[x]++;
    if (bb[x]<2) return;
    if (ps[x][0].se==ps[x][1].se) {
        tp00.insert(x);
    } else {
//        printf("01 ins %d\n",x);
        tp01.insert(x);
    }
}

int main() {
    scanf("%d%d",&n,&m);
    rep(i,1,m+1) {
        scanf("%i%i",a+i,b+i);
        if (a[i]==b[i]) continue;
        add(a[i],i,0);
        add(b[i],i,1);
        if (b[i]==0) bb[a[i]]++;
        else bb[b[i]]++;
    }
    set<int> fr;
    rep(i,1,m+1) if (a[i]==0) fr.insert(i);
    rep(i,1,n+1) {
        if (bb[i]<2) continue;
        if (ps[i][0].se==ps[i][1].se) {
            tp00.insert(i);
        } else {
            tp01.insert(i);
        }
    }
    rep(i,1,n+1) if (cnt[i][1]==2) {
        tp.insert(i);
        tp00.erase(i);
    }
    vector<PII> ans;
    while (1) {
        if (SZ(tp)&&SZ(fr)) {
            auto it1=tp.begin();
            auto it2=fr.begin();
            int f1=*it1,f2=*it2;
            ans.pb(mp(ps[f1][0].fi,f2));
            ans.pb(mp(ps[f1][1].fi,f2));
            ins(a[ps[f1][0].fi]);
            ins(a[ps[f1][1].fi]);
            tp.erase(it1);
            fr.erase(it2);
            continue;
        }
        if (SZ(tp00)) {
            auto it=tp00.begin();
            int x=*it;
            ans.pb(mp(ps[x][0].fi,ps[x][1].fi));
            fr.insert(ps[x][0].fi);
            tp00.erase(it);
            continue;
        }
        if (SZ(tp01)) {
            auto it=tp01.begin();
            int x=*it;
//            printf("01 %d\n",x);
            if (ps[x][0].se==0) swap(ps[x][0],ps[x][1]);
            ans.pb(mp(ps[x][0].fi,ps[x][1].fi));
            ins(a[ps[x][0].fi]);
            tp01.erase(it);
            continue;
        }
        break;
    }
    if (SZ(tp)+SZ(tp01)+SZ(tp00)>0) {
        puts("-1");
        return 0;
    }
    printf("%d\n",SZ(ans));
    rep(i,0,SZ(ans)) printf("%d %d\n",ans[i].fi,ans[i].se);
}

Compilation message (stderr)

Main.cpp: In function 'int main()':
Main.cpp:48:10: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   48 |     scanf("%d%d",&n,&m);
      |     ~~~~~^~~~~~~~~~~~~~
Main.cpp:50:14: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   50 |         scanf("%i%i",a+i,b+i);
      |         ~~~~~^~~~~~~~~~~~~~~~

• Subtask 1: 0 / 10
• Subtask 2: 10 / 10
• Subtask 3: 0 / 25
• Subtask 4: 0 / 15
• Subtask 5: 0 / 25
• Subtask 6: 0 / 15