Submission #856116

#	Time	Username	Problem	Language	Result	Execution time	Memory
856116		RiverFlow	Love Polygon (BOI18_polygon)	C++14	100 / 100	174 ms	25936 KiB

polygon

#include <bits/stdc++.h>

#define nl "\n"
#define no "NO"
#define yes "YES"
#define fi first
#define se second
#define vec vector
#define task "main"
#define _mp make_pair
#define ii pair<int, int>
#define sz(x) (int)x.size()
#define all(x) x.begin(), x.end()
#define evoid(val) return void(std::cout << val)
#define FOR(i, a, b) for(int i = (a); i <= (b); ++i)
#define FOD(i, b, a) for(int i = (b); i >= (a); --i)
#define unq(x) sort(all(x)); x.resize(unique(all(x)) - x.begin())

using namespace std;

template<typename U, typename V> bool maxi(U &a, V b) {
    if (a < b) { a = b; return 1; } return 0;
}
template<typename U, typename V> bool mini(U &a, V b) {
    if (a > b or a == -1) { a = b; return 1; } return 0;
}

const int N = (int)2e5 + 9;
const int mod = (int)1e9 + 7;

void prepare(); void main_code();

int main() {
    ios::sync_with_stdio(0); cin.tie(0); cout.tie(0);
    if (fopen(task".inp", "r")) {
        freopen(task".inp", "r", stdin);
        freopen(task".out", "w", stdout);
    }
    const bool MULTITEST = 0; prepare();
    int num_test = 1; if (MULTITEST) cin >> num_test;
    while (num_test--) { main_code(); }
}

void prepare() {};

int n, g[N], deg[N];

vector<int> adj[N];

stack<int> st;

bool on[N], on_cycle[N], vis[N];

void dfs(int u) {
    st.push(u); vis[u] = 1; on[u] = 1;
    int v = g[u];
    if (!vis[v]) {
        dfs(v);
    }
    if (on[v]) {
        while (st.size()) {
            int k = st.top(); on_cycle[k] = 1;
            st.pop(); on[k] = 0; if (k == v) break ;
        }
    }
    if (sz(st) and st.top() == u) st.pop();
    on[u] = 0;
}

int cnt[N], dp[N][2][2];

void main_code() {
    cin >> n; map<string, int> mp;
    if (n % 2 == 1) evoid(-1);
    for(int i = 1, cnt = 0; i <= n; ++i) {
        string x, y; cin >> x >> y;
        if (mp.find(x) == mp.end()) {
            mp[x] = ++cnt;
        }
        if (mp.find(y) == mp.end()) {
            mp[y] = ++cnt;
        }
        int a = mp[x], b = mp[y];
        g[a] = b;
    }
    FOR(i, 1, n) if (!vis[i]) dfs(i);

    FOR(i, 1, n) {
        ++deg[g[i]];
    }

    queue<int> q;
    int res = 0;
    FOR(i, 1, n) if (deg[i] == 0) {
        q.push(i);
    }
    vec<bool> c(n + 1, 0);
    while (!q.empty()) {
        int u = q.front(); q.pop();
        --deg[g[u]]; if (deg[g[u]] == 0) q.push(g[u]);
        if (!c[u]) {
            if (on_cycle[g[u]]) {
                ++cnt[g[u]];
                continue ;
            }
            ++res; if (!c[g[u]] and on_cycle[g[u]] == 0) c[g[u]] = 1;
        }
    }
//    FOR(i, 1, n) cout << c[i] << ' '; cout << nl << res << nl;
//    FOR(i, 1, n) cout << cnt[i] << ' '; cout << nl;
    vec<bool> mark(n + 1, 0);
    FOR(i, 1, n) if (on_cycle[i] and !mark[i]) {
        vec<int> cy;
        cy.push_back(i);
        for(int j = g[i]; j != i; j = g[j]) {
            cy.push_back(j);
        }
        for(int k : cy) {
            if (cnt[k] > 1) {
                res += cnt[k] - 1;
                cnt[k] = 1;
            }
            mark[k] = 1;
        }
        if (sz(cy) == 1) {
            ++res; continue ;
        }
        if (sz(cy) == 2) {
            for(int k : cy) res += cnt[k];
            continue ;
        }
//        for(int k : cy) cout << k << ' '; cout << nl;

        int m = sz(cy);

        FOR(i, 0, m) FOR(j, 0, 1) FOR(k, 0, 1) dp[i][j][k] = n;

        dp[0][0][0] = 1;
        dp[0][0][1] = cnt[ cy[0] ];
        dp[0][1][0] = cnt[ cy[0] ] + 1;

        FOR(i, 0, m - 3) FOR(j, 0, 1) FOR(k, 0, 1) {
            if (k == 0) {
                // no match (i, i + 1)
                mini(dp[i + 1][j][0], dp[i][j][k] + 1);
                mini(dp[i + 1][j][1], dp[i][j][k] + cnt[ cy[i + 1] ]);
            } else {
                mini(dp[i + 1][j][0], dp[i][j][k] + cnt[ cy[i + 1] ] + 1);
            }
        }

        // match (0, m - 1)
        mini(dp[m - 1][1][1], dp[m - 2][1][0] + cnt[ cy[m - 1] ]);

        // match (m - 1, m - 2)
        mini(dp[m - 1][0][0], dp[m - 2][0][1] + cnt[ cy[m - 1] ] + 1);

        // match (m - 1, it'child)
        mini(dp[m - 1][0][0], dp[m - 2][0][0] + 1);

        int l = n; FOR(j, 0, 1) FOR(k, 0, 1) l = min(l, dp[m - 1][j][k]);

        res += l;
    }
    cout << res;
}


/*     Let the river flows naturally     */

Compilation message (stderr)

polygon.cpp: In function 'int main()':
polygon.cpp:36:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   36 |         freopen(task".inp", "r", stdin);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~
polygon.cpp:37:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   37 |         freopen(task".out", "w", stdout);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~

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