Submission #393299

#	Time	Username	Problem	Language	Result	Execution time	Memory
393299		jainbot27	Love Polygon (BOI18_polygon)	C++17	100 / 100	83 ms	16216 KiB

polygon

#include <bits/stdc++.h>
using namespace std;

#define f first
#define s second
#define pb push_back
#define ar array
#define all(x) x.begin(), x.end()
#define siz(x) (int) x.size()
#define uid(a, b) uniform_int_distribution<int>(a, b)(rng)

#define FOR(i, a, b) for(int i=(a); i<(b); i++)
#define ROF(i, a, b) for(int i=(b-1); i>=(a); i--)
#define F0R(i, n) FOR(i, 0, n)
#define R0F(i, n) ROF(i, 0, n)
#define trav(x, y) for(auto&x:y)

using ll=long long;
using ld=long double;
using pii=pair<int, int>;
using pll=pair<ll, ll>;
using pli=pair<ll, int>;
using vi=vector<int>;
using vl=vector<ll>;
using vpii=vector<pii>;

template<class T> inline bool ckmin(T&a, const T&b) {return b<a?a=b,1:0;}
template<class T> inline bool ckmax(T&a, const T&b) {return b>a?a=b,1:0;}
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());

const char nl='\n';
const int mxN=1e5+10;
const int MOD=1e9+7;
const ll infLL=1e18;
const ld eps=1e-6;

int n; 
string s[mxN], t[mxN];
unordered_map<string, int> mp;
int a[mxN];
int deg[mxN];
int par[mxN], sz[mxN];
bool alive[mxN];
int used[mxN];
queue<int> q;
int ans=0;

int Find(int u){
    return par[u]=(par[u]==u?par[u]:Find(par[u]));
}
bool comb(int e1, int e2){
    e1=Find(e1); e2=Find(e2); 
    if(e1==e2) return 0;
    if(sz[e1]<sz[e2]) swap(e1, e2);
    sz[e1]+=sz[e2]; sz[e2]=0;
    par[e2]=e1;
    return 1;
}

int32_t main(){
    cin.tie(0)->sync_with_stdio(0);
    int n;
    cin >> n;
    if(n&1) {cout << "-1\n"; return 0;}
    F0R(i, n) par[i]=i, sz[i]=1;
    F0R(i, n)
        cin >> s[i] >> t[i], mp[s[i]]=i;
    F0R(i, n){
        a[i]=mp[t[i]];
        deg[a[i]]++;
        alive[i]=1;
    }    
    F0R(i, n){
        if(alive[i]&&a[i]!=i&&a[a[i]]==i){
            alive[a[i]]=0;
            alive[i]=0;
            deg[a[i]]--;
            deg[i]--;
        }
    }
    F0R(i, n)
        if(deg[i]==0){
            q.push(i);
        }       
    while(!q.empty()){
        auto T=q.front(); q.pop();
        assert(deg[T]==0);
        if(alive[T]==0) continue;
        if(alive[a[T]]==0) continue;
        alive[T]=0;
        alive[a[T]]=0;
        ans++;
        if(alive[a[a[T]]]) {
            deg[a[a[T]]]--;
            if(deg[a[a[T]]]==0)
                q.push(a[a[T]]);
        }
    }
    F0R(i, n){
        if(alive[i]&&alive[a[i]]){
            comb(a[i], i);
        }
    }
    F0R(i, n){
        if(alive[i]&&!used[Find(i)]){
            used[Find(i)]=1;
            ans+=(sz[Find(i)]+1)/2;
        }
    }
    cout << ans << nl;
}

• Subtask 1: 21 / 21
• Subtask 2: 25 / 25
• Subtask 3: 29 / 29
• Subtask 4: 25 / 25