Submission #1335489

#	Time	Username	Problem	Language	Result	Execution time	Memory
1335489		Hisu	Reachability (NOI25_reachability)	C++20	20 / 100	4 ms	1092 KiB

Main

#include <bits/stdc++.h>
using namespace std;

typedef long long ll;
#define ed "\n"
#define int long long

const int N = 2e5 + 5;
int n, l[N], u[N], v[N];

namespace sub2 {
    bool check() {
        return n <= 15;
    }

    vector<int> adj[N];

    void dfs(int u, int pa, int &res) {
        res++;
        for(int v : adj[u]) {
            if(v == pa) continue;
            dfs(v, u, res);
        }
    }

    void backtrack(int pos) {
        if(pos >= n) {
            bool check = true;
            for(int i = 1; i <= n; i++) {
                int res = 0;
                dfs(i, 0, res);
                if(res != l[i]) {
                    check = false;
                    break;
                }
            }

            if(check == true) {
                cout << "YES";
                exit(0);
            }
            return;
        }

        if(l[u[pos]] == l[v[pos]]) {
            adj[u[pos]].push_back(v[pos]);
            adj[v[pos]].push_back(u[pos]);
            backtrack(pos + 1);
            adj[u[pos]].pop_back();
            adj[v[pos]].pop_back();
        }

        if(l[u[pos]] > l[v[pos]]) {
            adj[u[pos]].push_back(v[pos]);
            backtrack(pos + 1);
            adj[u[pos]].pop_back();
        }

        if(l[u[pos]] < l[v[pos]]) {
            adj[v[pos]].push_back(u[pos]);
            backtrack(pos + 1);
            adj[v[pos]].pop_back();
        }

        backtrack(pos + 1);
    }

    void solve() {
        backtrack(1);
        cout << "NO";
    }
}

namespace sub3 {
    bool check() {
        for(int i = 2; i <= n; i++) if(l[i] != l[i - 1]) return false;
        return true;
    }

    vector<int> adj[N];

    int dfs(int u, int pa) {
        int res = 1;
        for(int v : adj[u]) {
            if(v == pa) continue;
            res += dfs(v, u);
        }
        if(res > l[1]) {
            cout << "NO";
            exit(0);
        }

        if(res == l[1]) res = 0;

        return res;
    }

    void solve() {
        // goi L = l[1] = l[2] = .. = l[n]
        // n % L != 0 => NO
        if(n % l[1] != 0) {
            cout << "NO";
            return;
        }

        for(int i = 1; i < n; i++) {
            adj[u[i]].push_back(v[i]);
            adj[v[i]].push_back(u[i]);
        }

        if(dfs(1, 0) > 0) {
            cout << "NO";
            return;
        }

        cout << "YES";
    }
}

void solve(int iTest) {
    cin >> n;
    for(int i = 1; i <= n; i++) cin >> l[i];
    for(int i = 1; i < n; i++) cin >> u[i] >> v[i];

    if(sub2::check()) {
        sub2::solve();
        return;
    }

    if(sub3::check()) { 
        sub3::solve();
        return;
    }
}

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

    #define TASK "main"
    if(fopen(TASK ".inp", "r")) {
        freopen(TASK ".inp", "r", stdin);
        freopen(TASK ".out", "w", stdout);
    }
    else if(fopen("main.inp", "r")) {
        freopen("main.inp", "r", stdin);
        freopen("main.out", "w", stdout);
    }

    int T = 1;
    // cin >> T;
    for(int iTest = 1; iTest <= T; iTest++) {
        solve(iTest);
    }
}

Compilation message (stderr)

Main.cpp: In function 'int main()':
Main.cpp:142:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
  142 |         freopen(TASK ".inp", "r", stdin);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~
Main.cpp:143:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
  143 |         freopen(TASK ".out", "w", stdout);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~
Main.cpp:146:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
  146 |         freopen("main.inp", "r", stdin);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~
Main.cpp:147:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
  147 |         freopen("main.out", "w", stdout);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~

• Subtask 0: 0 / 0
• Subtask 1: 4 / 4
• Subtask 2: 5 / 5
• Subtask 3: 11 / 11
• Subtask 4: 0 / 10
• Subtask 5: 0 / 45
• Subtask 6: 0 / 25