Submission #934062

#	Time	Username	Problem	Language	Result	Execution time	Memory
934062		sysia	Newspapers (CEOI21_newspapers)	C++17	0 / 100	0 ms	348 KiB

newspapers

//Sylwia Sapkowska
#include <bits/stdc++.h>
#pragma GCC optimize("O3", "unroll-loops")
using namespace std;

void __print(int x) {cerr << x;}
void __print(long long x) {cerr << x;}
void __print(long double x) {cerr << x;}
void __print(char x) {cerr << "'" << x << "'";}
void __print(const char *x) {cerr << '"' << x << '"';}
void __print(const string &x) {cerr << '"' << x << '"';}
void __print(bool x) {cerr << (x ? "true" : "false");}

template<typename T, typename V>
void __print(const pair<T, V> &x) {cerr << '{'; __print(x.first); cerr << ", "; __print(x.second); cerr << '}';}
template<typename T>
void __print(const T &x) {int f = 0; cerr << '{'; for (auto &i: x) cerr << (f++ ? ", " : ""), __print(i); cerr << "}";}
void _print() {cerr << "]\n";}
template <typename T, typename... V>
void _print(T t, V... v) {__print(t); if (sizeof...(v)) cerr << ", "; _print(v...);}
#ifdef LOCAL
#define debug(x...) cerr << "[" << #x << "] = ["; _print(x)
#else
#define debug(x...)
#endif

#define int long long
typedef pair<int, int> T;
const int oo = 1e18, oo2 = 1e9+7, K = 30;
const int mod = 998244353;

void solve(){
    int n, m; cin >> n >> m;
    if (m >= n){
        cout << "NO\n";
        return;
    } 
    vector<vector<int>>g(n+1);
    for (int i = 1; i<n; i++){
        int a, b; cin >> a >> b;
        g[a].emplace_back(b);
        g[b].emplace_back(a);
    }
    vector<int>depth(n+1), par(n+1);
    function<void(int, int, int)>dfs = [&](int v, int pa, int pa2=-1){
        par[v] = pa;
        for (auto x: g[v]){
            if (x == pa || x == pa2) continue;
            depth[x] = depth[v]+1;
            dfs(x, v, -1);
        }
    };
    dfs(1, 1, -1);
    T now = {-oo, -oo};
    for (int v = 1; v <= n; v++) now = max(now, T{depth[v], v});
    int L = now.second;
    depth[L] = 0;
    dfs(L, L, -1);
    now = {-oo, -oo};
    for (int v = 1; v <= n; v++) now = max(now, T{depth[v], v});
    int R = now.second;
    vector<int>curr;
    int v = R;
    while (1){
        curr.emplace_back(v);
        if (v == L) break;
        v = par[v];
    }
    reverse(curr.begin(), curr.end());
    debug(curr);
    int s = (int)curr.size();
    for (int rep = 0; rep < s; rep++){
        int v = curr[rep];
        depth[v] = 0;
        dfs(v, (rep ? curr[rep-1] : -1), (rep+1<s ? curr[rep+1] : -1));
    }
    debug(depth);
    if (*max_element(depth.begin(), depth.end()) > 2) {
        cout << "NO\n";
        return;
    }
    //fajna struktura drzewa miau
    cout << "YES\n";
}


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

    int t = 1;
    //cin >> t;
    while (t--) solve();

    return 0;
}

• Subtask 1: 0 / 12
• Subtask 2: 0 / 8
• Subtask 3: 0 / 80