Submission #341337

#	Time	Username	Problem	Language	Result	Execution time	Memory
341337		IZhO_2021_I_want_Silver	Shymbulak (IZhO14_shymbulak)	C++14	0 / 100	60 ms	11500 KiB

shymbulak

#include <iostream>
#include <algorithm>
#include <vector>
#include <cmath>
#include <set>
#include <map>
#include <iomanip>
#include <cassert>
#include <stack>
#include <queue>
#include <deque>
//#include <ext/pb_ds/assoc_container.hpp>
//#include <ext/pb_ds/tree_policy.hpp>-

using namespace std;
//using namespace __gnu_pbds;

typedef long long ll;
typedef pair <int, int> pii;
typedef pair <ll, ll> pll;

// template<typename T> using ordered_set = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
//  order_of_key (k) : Number of items strictly smaller than k .
//  find_by_order(k) : K-th element in a set (counting from zero).
#define sz(a) (int)a.size()
#define all(a) a.begin(), a.end()
#define pb push_back
#define ppb pop_back
#define mkp make_pair
#define F first
#define S second
#define lb lower_bound
#define ub upper_bound
#define show(a) cerr << #a <<" -> "<< a <<" "
#define nl cerr <<"\n"
//#define int ll

const int N = 5005;
const int oo = 1e9 + 5;

int n, d[N][N], mx, ans, cnt[N], cycle[N];
vector <int> g[N];
queue <int> q;
bool was[N], bad;

void dfs(int v, int col) {
    was[v] = 1;
    cycle[v] = col;
    for (int to : g[v]) {
        if (was[to]) { continue; }
        if (!cnt[to]) { dfs(to, col); }
    }
}

void solve() {
    cin >> n;
    for (int i = 1; i <= n; ++i) {
        int a, b;
        cin >> a >> b;
        g[a].pb(b);
        g[b].pb(a);
    }
    for (int i = 1;  i <= n; ++i) {
        cnt[i] = sz(g[i]);
        if (sz(g[i]) == 1) { q.push(i); }
    }
    while(sz(q)) {
        int v = q.front(); q.pop();
        --cnt[v];

        for (int to : g[v]) {
            if (cnt[to] > 1) { --cnt[to];  }
            if (cnt[to] == 1) { q.push(to); }
        }
    }
    int len = 0;
    for (int i = 1; i <= n; ++i) {
        if (cnt[i]) { ++len; } assert(cnt[i] == 0 || cnt[i] == 2);
    }
    for (int i = 1; i <= n; ++i) {
        if (cycle[i]) { continue; }
        if (cnt[i] == 2) {
            dfs(i, i);
        }
    }
    for (int i = 1; i <= n; ++i) {
        for (int j = 1; j <= n; ++j) { d[i][j] = oo; }
        d[i][i] = 0;
        q.push(i);
        while (sz(q)) {
            int v = q.front();
            q.pop();
            for (int to : g[v]) {
                if (d[i][to] >  d[i][v] + 1) {
                    d[i][to] = d[i][v] + 1;
                    q.push(to);
                }
            }
        }
        for (int j = 1; j <= n; ++j) { mx = max(mx, d[i][j]); }
    }
    for (int i = 1; i <= n; ++i) {
        for (int j = 1; j <= n; ++j) {
            if (mx == d[i][j]) {
                ++ans;
                if (d[ cycle[i] ][ cycle[j] ] != len / 2) { bad = 1; }
            }
        }
    }
    if ((len & 1) || bad) { ans >>= 1; }
    cout << ans;
}

 main () {
	ios_base::sync_with_stdio(false);
	cin.tie(NULL);
	int tests = 1;
	//cin >> tests;
	while (tests --) {
		solve();
	}
	return 0;
}
/*
    Just Chalish!
7
1 4
2 4
3 4
4 5
5 6
6 7
5 7

8
1 2
1 3
4 3
4 2
3 5
5 6
4 7
7 8
*/

Compilation message (stderr)

shymbulak.cpp:114:8: warning: ISO C++ forbids declaration of 'main' with no type [-Wreturn-type]
  114 |  main () {
      |        ^

• Subtask 1: 0 / 30
• Subtask 2: 0 / 20
• Subtask 3: 0 / 50