Submission #1200598

#	Time	Username	Problem	Language	Result	Execution time	Memory
1200598		InvMOD	우호 조약 체결 (JOI14_friends)	C++17	100 / 100	37 ms	6472 KiB

friends

#include<bits/stdc++.h>

using namespace std;

#define fi first
#define se second
#define pb push_back
#define eb emplace_back

#define vi vector<int>
#define pi pair<int,int>
#define sz(v) (int)(v).size()
#define all(v) (v).begin(), (v).end()
#define compact(v) (v).erase(unique(all(v)), (v).end())

template<class T> using upq = priority_queue<T, vector<T>, greater<T>>;
template<class T> int lwrbound(const vector<T>& a, const T& b, const int s = 0){return int(lower_bound(s + all(a), b) - a.begin());}
template<class T> int uprbound(const vector<T>& a, const T& b, const int s = 0){return int(upper_bound(s + all(a), b) - a.begin());}

#define FOR(i, a, b) for(int i = (a); i <= (b); i++)
#define ROF(i, a, b) for(int i = (a); i >= (b); i--)
#define sumof(x) accumulate(all(x), 0ll)
#define dbg(x) "[" << #x " = " << (x) << "]"
#define el "\n"

using ll = long long;
using ld = long double;

template<class T> bool ckmx(T& a, const T b){return (a < b ? a = b, true : false);}
template<class T> bool ckmn(T& a, const T b){return (a > b ? a = b, true : false);}

const int N = 2e5 + 5;
const int MOD = 1e9 + 7;
const ll INF = numeric_limits<ll>::max() / 8;

struct DSU{
    vector<int> par;

    DSU(int n = 0): par(n + 1, - 1) {}

    int asc(int x){
        return par[x] < 0 ? x : par[x] = asc(par[x]);
    }

    void join(int u, int v){
        u = asc(u), v = asc(v);

        if(u != v){
            if(par[u] > par[v]) swap(u, v);

            par[u] += par[v], par[v] = u;
        }
    }

    bool isPar(int x){
        return asc(x) == x;
    }

    int gsz(int x){return -par[asc(x)];}
};

void Main()
{
    int n,m; cin >> n >> m;

    vector<vi> adj(n + 1, vi());
    FOR(i, 1, m){
        int u,v; cin >> u >> v;
        adj[u].eb(v);
    }

    DSU dsu(n); queue<int> q;

    vector<bool> pushQ(n + 1, false);
    FOR(i, 1, n)if(sz(adj[i]) > 1){
        int pNode = -1;
        for(int v : adj[i]){
            if(pNode == -1) pNode = v;
            else{
                dsu.join(pNode, v);

                if(!pushQ[v]) q.push(v), pushQ[v] = true;
            }
        }
        if(!pushQ[pNode]) q.push(pNode), pushQ[pNode] = true;
    }

    // expand new component
    while(sz(q)){
        int x = q.front(); q.pop();

        for(int v : adj[x]){
            dsu.join(x, v);
            if(!pushQ[v]){
                q.push(v);
                pushQ[v] = true;
            }
        }
    }

    ll ans = 0;
    FOR(i, 1, n) if(dsu.isPar(i)){
        if(dsu.gsz(i) == 1){
            ans = ans + sz(adj[i]);
            //cout << "Node: " << i <<" " << sz(adj[i]) << el;
        }
        else{
            ll sz_comp = dsu.gsz(i);
            //cout << "Comp: " << i <<" " << sz_comp << el;
            ans = ans + 1ll * sz_comp * (sz_comp - 1);
        }
    }

    cout << ans << el;
}

int32_t main()
{
    ios_base::sync_with_stdio(0);
    cin.tie(0); cout.tie(0);

    #define name "InvMOD"
    if(fopen(name".INP", "r")){
        freopen(name".INP", "r", stdin);
        freopen(name".OUT", "w", stdout);
    }

    int t = 1; while(t--) Main();
    return 0;
}

/*
    a -> b
    a -> c

    create b <-> c

    d -> a
    d -> c

    create a <-> c

    b -> d => (d <-> a, c)
    d -> b => (d <-> a, c)

    if a component has size > 1, it can connect to any other component or node that it has an edge to

    // total edge of a component can be calculate by:
    size(component) * (size(component) - 1)

    how about others node connect to a component ?

    ans: it still need 2 edges to connect to that component

    so we will create all component and calculate the answer
    with component that has size = 1 it does not contribute any new edge
*/

Compilation message (stderr)

friends.cpp: In function 'int32_t main()':
friends.cpp:124:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
  124 |         freopen(name".INP", "r", stdin);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~
friends.cpp:125:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
  125 |         freopen(name".OUT", "w", stdout);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~

• Subtask 1: 5 / 5
• Subtask 2: 30 / 30
• Subtask 3: 65 / 65