Submission #1298624

#	Time	Username	Problem	Language	Result	Execution time	Memory
1298624		nqc	Love Polygon (BOI18_polygon)	C++20	75 / 100	412 ms	103092 KiB

polygon

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

#define fi first
#define se second
#define ll long long
#define ull unsigned long long
#define pii pair<int, int>
#define pll pair<ll, ll>
#define pli pair<ll, int>
#define debug(x) cout << #x << " = " << x << '\n'
#define all(a) a.begin(), a.end()
#define SZ(a) (int)(a).size()

const int N = 1e6 + 5;
const int mod = 1e9 + 7;
const ll inf64 = 3e18;
const int inf32 = 2e9 + 5;

int n, g[N];

namespace sub1 {
    int dp[1 << 20][25];

    void sol() {
        memset(dp, 63, sizeof dp);
        dp[0][0] = 0;
        for(int msk = 1; msk < (1 << n); msk++) {
            int popcnt = __builtin_popcount(msk);
            if(popcnt == 1) {
                int p = -1;
                for(int i = 0; i < n; i++) if(msk >> i & 1) {
                    p = i;
                    break;
                }
                dp[msk][p] = 0;
                continue;
            }

            if(popcnt & 1) {
                for(int i = 0; i < n; i++) if(msk >> i & 1)
                    dp[msk][i] = min(dp[msk][i], dp[msk ^ (1 << i)][0]);
            }
            else {
                for(int i = 0; i < n; i++) if(msk >> i & 1) {
                    for(int j = 0; j < n; j++) if(i != j && (msk >> j & 1)) 
                        dp[msk][0] = min(dp[msk][0], dp[msk ^ (1 << i)][j] + (g[i + 1] != j + 1) + (g[j + 1] != i + 1));
                }
            }
        }
        cout << dp[(1 << n) - 1][0];
    }
};

namespace sub2 {
    bool check() {
        vector<bool> chk(n + 3, 0);
        for(int i = 1; i <= n; i++) 
            chk[g[i]] = true;
        for(int i = 1; i <= n; i++) 
            if(!chk[i]) return false;
        return true;
    }

    bool vis[N];
    int cnt;

    void dfs(int u) {
        cnt++, vis[u] = true;
        if(!vis[g[u]]) dfs(g[u]);
    }

    void sol() {
        int ans = 0;
        for(int i = 1; i <= n; i++) if(!vis[i]) {
            cnt = 0;
            dfs(i);
            if(cnt != 2) ans += (cnt + 1) / 2;
        }
        cout << ans << '\n';
    }
}

namespace sub3 {
    int par[N], dp[N][2], cnt;
    vector<int> child[N];

    void dfs(int u) {
        cnt++;
        for(int v : child[u]) {
            dfs(v);
            dp[u][0] += max(dp[v][0], dp[v][1]);
        }
        for(int v : child[u]) 
            dp[u][1] = max(dp[u][1], dp[u][0] - max(dp[v][0], dp[v][1]) + dp[v][0] + 1);

        // debug(u);
        // debug(dp[u][0]);
        // debug(dp[u][1]);
    }

    void sol() {
        for(int i = 1; i <= n; i++) {
            par[i] = g[i];
            if(par[i] != i) child[par[i]].push_back(i);
        }

        int ans = 0;
        for(int i = 1; i <= n; i++) if(par[i] == i) {
            cnt = 0;
            dfs(i);
            int mx = max(dp[i][0], dp[i][1]);
            ans += mx + (cnt - 2 * mx);
        }
        cout << ans << '\n';
    }
}

void solve() {
    int q; cin >> q;
    map<string, int> mp;
    for(int i = 1; i <= q; i++) {
        string s, t; cin >> s >> t;
        if(!mp.count(s)) mp[s] = ++n;
        if(!mp.count(t)) mp[t] = ++n;

        g[mp[s]] = mp[t];
    }

    if(n & 1) {
        cout << -1;
        return;
    }

    if(n <= 20) return sub1::sol();
    if(sub2::check()) return sub2::sol();
    return sub3::sol();
}

int main() {
    auto start = chrono::steady_clock::now();

    ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
    if(fopen("input.txt", "r")) {
        freopen("input.txt", "r", stdin);
        freopen("output.txt", "w", stdout);
    }
    int test = 1; 
    // cin >> test;
    while(test--) solve();
    
    chrono::duration<double> elapsed {chrono::steady_clock::now() - start};
    cerr << "\n>> Runtime: " << elapsed.count() << "s\n";
}

Compilation message (stderr)

polygon.cpp: In function 'int main()':
polygon.cpp:145:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
  145 |         freopen("input.txt", "r", stdin);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~
polygon.cpp:146:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
  146 |         freopen("output.txt", "w", stdout);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~

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