Submission #997300

#	Time	Username	Problem	Language	Result	Execution time	Memory
997300		whatthemomooofun1729	Love Polygon (BOI18_polygon)	C++17	100 / 100	335 ms	36296 KiB

polygon

#include <iostream>
#include <algorithm>
#include <utility>
#include <vector>
#include <stack>
#include <map>
#include <queue>
#include <set>
#include <unordered_set>
#include <unordered_map>
#include <cstring>
#include <cmath>
#include <functional>
#include <cassert>
#include <iomanip>
#include <numeric>
#include <bitset>
#include <sstream>
#include <chrono>
#include <random>

#define ff first
#define ss second
#define PB push_back
#define sz(x) int(x.size())
#define rsz resize
#define fch(xxx, yyy) for (auto xxx : yyy) // abusive notation
#define all(x) (x).begin(),(x).end()
#define eps 1e-9

// more abusive notation (use at your own risk):
//#define int ll

using namespace std;
typedef long long ll;
typedef long double ld;
typedef unsigned long long ull;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
using vi = vector<int>;
using vll = vector<ll>;

// debugging
void __print(int x) {std::cerr << x;}
void __print(ll x) {std::cerr << x;} /* remember to uncomment this when not using THE MACRO */
void __print(unsigned x) {std::cerr << x;}
void __print(ull x) {std::cerr << x;}
void __print(float x) {std::cerr << x;}
void __print(double x) {std::cerr << x;}
void __print(ld x) {std::cerr << x;}
void __print(char x) {std::cerr << '\'' << x << '\'';}
void __print(const char *x) {std::cerr << '\"' << x << '\"';}
void __print(const string& x) {std::cerr << '\"' << x << '\"';}
void __print(bool x) {cerr << (x ? "true" : "false");}
template<typename T, typename V> void __print(const pair<T, V> &x) {std::cerr << '{'; __print(x.ff); std::cerr << ", "; __print(x.ss); std::cerr << '}';}
template<typename T> void __print(const T& x) {int f = 0; std::cerr << '{'; for (auto &i: x) std::cerr << (f++ ? ", " : ""), __print(i); std::cerr << "}";}
void _print() {std::cerr << "]\n";}
template <typename T, typename... V> void _print(T t, V... v) {__print(t); if (sizeof...(v)) std::cerr << ", "; _print(v...);}
void println() {std::cerr << ">--------------------<" << endl;}
#ifndef ONLINE_JUDGE
#define debug(x...) cerr << "[" << #x << "] = ["; _print(x)
#else
#define debug(x...)
#endif

// templates
template <class T> bool ckmin(T &a, const T &b) {return b<a ? a = b, 1 : 0;}
template <class T> bool ckmax(T &a, const T &b) {return b>a ? a = b, 1 : 0;}
template <class T> using gr = greater<T>;
template <class T> using vc = vector<T>;
template <class T> using p_q = priority_queue<T>;
template <class T> using pqg = priority_queue<T, vc<T>, gr<T>>;
template <class T1, class T2> using pr = pair<T1, T2>;
mt19937_64 rng_ll(chrono::steady_clock::now().time_since_epoch().count());
int rng(int M) {return (int)(rng_ll()%M);} /*returns any random number in [0, M) */

// const variables
constexpr int INF = (int)2e9;
constexpr int MOD = 998244353;
constexpr ll LL_INF = (ll)3e18;
constexpr int mod = (int)1e9 + 7;
constexpr ll inverse = 500000004LL; // inverse of 2 modulo 1e9 + 7

void setIO(const string& str) {// fast input/output
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    if (str.empty()) return;
    freopen((str + ".in").c_str(), "r", stdin);
    freopen((str + ".out").c_str(), "w", stdout);
}

// f: f[u] = the one u loves
int N, cnt = 1;
map<string, int> mp; // mapping strings to integer indices
vc<vi> adj; // for each v, keep track of all u such that f[u] = v
vc<vi> $, comps; // $ is the undirected version of the graph
// comps keeps track of the vertices in each component
vi dp[2], vst, f, cc;
// cc[v] = component that v is in

void dfs(int v) {
    dp[0][v] = 0, dp[1][v] = 1;
    vst[v] = 1;
    vi children; // children of v
    fch(u, adj[v]) if (!vst[u]) {
            dfs(u);
            children.PB(u);
            dp[1][v] += dp[0][u];
        }
    if (sz(children) == 0) return;
    int C = sz(children);
    vi psum(C), ssum(C);
    for (int i = 0; i < C; ++i) {
        psum[i] = (i > 0 ? psum[i - 1] : 0) + dp[0][children[i]];
    }
    for (int i = C-1; i >= 0; --i) {
        ssum[i] = (i < C - 1 ? ssum[i + 1] : 0) + dp[0][children[i]];
    }
    for (int i = 0; i < C; ++i) {
        ckmax(dp[0][v], dp[1][children[i]] + (i > 0 ? psum[i - 1] : 0) + (i < C - 1 ? ssum[i + 1] : 0));
    }
}

void undo(int v) {
    for (int i = 0; i < sz(comps[cc[v]]); ++i) { // resetting all visited values in component to 0
        vst[comps[cc[v]][i]] = 0;
    }
}

void why_not(int v) {
    for (int i = 0; i < sz(comps[cc[v]]); ++i) { // set them all to 1
        vst[comps[cc[v]][i]] = 1;
    }
}

void dfs1(int v) {
    fch(u, $[v]) if (cc[u] != cc[v]) { // finding connected components
            cc[u] = cc[v];
            dfs1(u);
        }
}

signed main() { // TIME YOURSELF !!!
    setIO("");
    cin >> N;
    if (N & 1) {
        cout << "-1\n";
        return 0;
    }
    adj.rsz(N+1), dp[0].rsz(N+1, 0), dp[1].rsz(N+1, 1), vst.rsz(N+1), f.rsz(N+1), cc.rsz(N+1, -1), comps.rsz(N+1);
    $.rsz(N + 1);
    for (int i = 0; i < N; ++i) {
        string a, b;
        cin >> a >> b;
        if (mp[a] == 0) mp[a] = cnt++;
        if (mp[b] == 0) mp[b] = cnt++;
        adj[mp[b]].PB(mp[a]);
        $[mp[b]].PB(mp[a]);
        $[mp[a]].PB(mp[b]);
        f[mp[a]] = mp[b];
    }
    { // finding the connected components
        for (int i = 1; i <= N; ++i) {
            if (cc[i] == -1) {
                cc[i] = i;
                dfs1(i);
            }
        }
        for (int i = 1; i <= N; ++i) {
            comps[cc[i]].PB(i);
        }
    }
    int ans = 0;
    for (int i = 1; i <= N; ++i) {
        if (!vst[i]) {
            int t = f[i], h = f[f[i]]; // find the cycle
            while (t != h) {
                t = f[t];
                h = f[f[h]];
            }
            int L = 1;
            t = f[t];
            while (t != h) {
                L++;
                t = f[t];
            }
            if (L == 1) { // self-loop
                vst[t] = 1;
                dfs(t);
                ans += dp[0][t]; // t cannot be in the set
            } else { // not a self-loop
                int res = 0;
                int s = f[t];
                // 2: (t, f[t]) are not connected
                dfs(t);
                ckmax(res, dp[0][t]);
                undo(t);
                // 1: (t, f[t]) are connected
                if (L > 2) {
                    vst[t] = vst[s] = 1;
                    int temp = t;
                    t = f[s];
                    while (f[t] != temp) {
                        t = f[t];
                    }
                    dfs(t); // do DP over all vertices in the cycle excluding (t, s) and also the
                    // subtrees with each such vertex
                    int sum = dp[0][t] + 1;
                    t = temp;
                    // now DFS over all vertices that are not in the cycle but have f[u] = t or s
                    fch(u, adj[t]) if (!vst[u]) {
                            dfs(u);
                            sum += dp[0][u]; // cannot be in the set
                        }
                    fch(u, adj[s]) if (!vst[u]) {
                            dfs(u);
                            sum += dp[0][u]; // cannot be in the set
                        }
                    ckmax(res, sum);
                } else if (L == 2) {
                    vst[t] = vst[s] = 1;
                    int sum = 2;
                    // similar logic here
                    fch(u, adj[t]) if (!vst[u]) {
                            dfs(u);
                            sum += dp[0][u];
                        }
                    fch(u, adj[s]) if (!vst[u]) {
                            dfs(u);
                            sum += dp[0][u];
                        }
                    ckmax(res, sum);
                }
                ans += res;
            }
            why_not(i);
        }
    }
    assert(ans <= N);
    cout << N - ans << '\n';
    return 0;
}

// TLE -> TRY NOT USING DEFINE INT LONG LONG
// CE -> CHECK LINE 45
// 5000 * 5000 size matrices are kinda big (potential mle)
// Do something, start simpler

Compilation message (stderr)

polygon.cpp: In function 'void setIO(const string&)':
polygon.cpp:88:12: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   88 |     freopen((str + ".in").c_str(), "r", stdin);
      |     ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
polygon.cpp:89:12: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   89 |     freopen((str + ".out").c_str(), "w", stdout);
      |     ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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