Submission #541618

#	Time	Username	Problem	Language	Result	Execution time	Memory
541618		Lobo	Love Polygon (BOI18_polygon)	C++17	54 / 100	161 ms	30632 KiB

polygon

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

const long long inf = (long long) 1e18 + 10;
const int inf1 = (int) 1e9 + 10;
#define int long long
#define dbl long double
#define endl '\n'
#define sc second
#define fr first
#define mp make_pair
#define pb push_back
#define all(x) x.begin(), x.end()

const int maxn = 1e5+10;

int n, nx[maxn], mark[maxn], markc[maxn], dp[maxn][2];
string nxstring[maxn];
vector<int> ginv[maxn];

int dfscyc(int u) {
    if(markc[u]) return u;
    markc[u] = 1;
    return dfscyc(nx[u]);
}

void dfs(int u) {
    int mn = inf;
    mark[u] = 1;

    for(auto v : ginv[u]) {
        if(mark[v]) continue;
        dfs(v);

        dp[u][0]+= min(dp[v][1],dp[v][0]+1);
        mn = min(mn, dp[v][0] - min(dp[v][1],dp[v][0]+1));
    }

    dp[u][1] = dp[u][0]+mn+1;
    // cout << u << " " << dp[u][0] << " " << dp[u][1] << endl;
}

void solve() {
    cin >> n;

    map<string,int> cc;
    for(int i = 1; i <= n; i++) {
        string s1,s2; cin >> s1 >> s2;

        cc[s1] = i;
        nxstring[i] = s2;
    }

    if(n%2 == 1) {
        cout << -1 << endl;
        return;
    }

    for(int i = 1; i <= n; i++) {
        nx[i] = cc[nxstring[i]];
        // cout << i << " " << nx[i] << endl;
        ginv[nx[i]].pb(i);
    }

    int ans = 0;
    for(int i = 1; i <= n; i++) {
        if(mark[i]) continue;
        int rt = dfscyc(i);
        // cout << rt << " root " << endl;
        dfs(rt);


        if(nx[rt] != rt && nx[nx[rt]] == rt) ans+= 0;
        else ans+= min(dp[rt][1],dp[rt][0]+1);
    }

    cout << ans << endl;

}

int32_t main() {
    ios::sync_with_stdio(false); cin.tie(0);

    // freopen("in.in", "r", stdin);
    // freopen("out.out", "w", stdout);

    int tt = 1;
    // cin >> tt;
    while(tt--) solve();

}

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