Submission #434001

#	Time	Username	Problem	Language	Result	Execution time	Memory
434001		HediChehaidar	Love Polygon (BOI18_polygon)	C++17	29 / 100	312 ms	16072 KiB

polygon

/*
ID: hedichehaidar
TASK: photo
LANG: C++11
*/
#include<bits/stdc++.h>
typedef long long ll;
typedef unsigned long long ull;
typedef long double ld;
typedef double db;
ll gcd(ll a , ll b) {return b ? gcd(b , a % b) : a ;} // greatest common divisor (PGCD)
ll lcm(ll a , ll b) {return (a * b) / gcd(a , b);} // least common multiple (PPCM)
#define ss second
#define ff first
#define all(x) (x).begin() , (x).end()
#define pb push_back
#define vi vector<int>
#define vii vector<pair<int,int>>
#define vl vector<ll>
#define vll vector<pair<ll,ll>>
#define pii pair<int,int>
#define pll pair<ll,ll>
#define pdd  pair<double,double>
#define vdd  vector<pdd>
#define dte  tuple<double , double , double>
using namespace std;
const int INF = 1000*1000*1000; // 1 e 9
const int MOD = INF + 7;
const double EPS = 0.000000001; // 1 e -9
const ll inf = (ll)1e18;

int n;
map<string  , int> m;
vi adj[(int)1e5 + 10];
bool vis[(int)1e5 + 10];
vi ts;
void dfs(int pos){
    if(vis[pos]) return ;
    vis[pos] = true;
    for(auto c : adj[pos]) dfs(c);
    ts.pb(pos);
}
int main() {
    //ifstream fin ("race.in");
    //ofstream fout ("race.out");
    ios::sync_with_stdio(false);cin.tie(0);cout.tie(0);
    cin>>n;
    if(n % 2) return cout << -1 << endl,0;
    int cur = 0;
    for(int i = 0 ; i < n ; i++){
        string a , b ; cin>>a>>b;
        if(m.find(a) == m.end()){
            m[a] = cur; cur++;
        }
        if(m.find(b) == m.end()){
            m[b] = cur; cur++;
        }
        int u = m[a] , v = m[b];
        adj[u].pb(v);
    }
    for(int i = 0 ; i < n ; i++){
        if(!vis[i]) dfs(i);
    }
    reverse(all(ts));
    memset(vis , 0 , sizeof vis);
    int ans = 0;
    for(int i = 0 ; i < n ; i++){
        int pos = ts[i];
        if(vis[pos]) continue;
        vis[pos] = true;
        int c = adj[pos][0];
        vis[c] = true;
        ans++;
    }
    cout << ans << "\n";
    return 0;
}

/*
    Think of : BS / DFS / BFS / SSSP / SCC / MSP / MAX FLOW / TOPSORT / LCA / MATRIX / DP(bitmask) / 2 POINTERS / SEG TREE / MATH / UN FIND / MO
    Read the statement CAREFULLY !!
    Make a GREADY APPROACH !!!! (start from highest / lowest)
    Make your own TESTS !!
    Be careful from CORNER CASES !
*/

• Subtask 1: 0 / 21
• Subtask 2: 0 / 25
• Subtask 3: 29 / 29
• Subtask 4: 0 / 25