Submission #630034

#	Time	Username	Problem	Language	Result	Execution time	Memory
630034		Vladth11	Star Trek (CEOI20_startrek)	C++14	38 / 100	141 ms	22196 KiB

startrek

#include <bits/stdc++.h>
#define C 1
#define P 0
#define debug(x) cerr << #x << " " << x << "\n"
#define debugs(x) cerr << #x << " " << x << " "

using namespace std;
typedef long long ll;
typedef pair <ll, ll> pii;
typedef pair <long double, pii> muchie;

const ll NMAX = 100001;
const ll VMAX = 101;
const ll INF = (1LL << 60);
const ll MOD = 1000000007;
const ll BLOCK = 447;
const ll base = 117;
const ll nr_of_bits = 18;
const ll inv2 = 500000004;

vector <ll> v[NMAX];
ll col[NMAX];
ll children[NMAX][2];
ll maximal[NMAX];
ll rosii[NMAX];
ll criticals[NMAX];
ll adv[NMAX];
ll sumR[NMAX][2];

void DFS(ll node, ll p){
    col[node] = P;
    for(auto x : v[node]){
        if(x == p) continue;
        DFS(x, node);
        children[node][col[x]]++;
    }
    if(children[node][C] == (ll)v[node].size() - (p != 0)){
        col[node] = P;
    }else{
        col[node] = C;
    }
    if(col[node] == P)
        rosii[node] = 1;
    for(auto x : v[node]){
        if(x == p) continue;
        if(col[node] != col[x] && children[node][C] >= (ll)v[node].size() - (p != 0) - 1){
            rosii[node] += rosii[x];
        }
        sumR[node][col[x]] += rosii[x];
    }
}

ll perdanti = 0;

void bagaR(int node, int p){
    rosii[node] = (col[node] == P);
    if(children[node][C] >= (ll)v[node].size() - (p != 0) - 1) { /// mereu facem bagaR pentru root
        rosii[node] += sumR[node][P + C - col[node]];
    }
}

void Rerooting(ll node, ll p){
    adv[node] = col[node];
    criticals[node] = rosii[node];
    if(adv[node] == P)
        perdanti++;
    for(auto x : v[node]){
        if(x == p) continue;
        ll cx = col[x], cnode = col[node];
        children[node][col[x]]--;
        sumR[node][col[x]] -= rosii[x];
        if(children[node][C] == v[node].size() - 1){
            col[node] = P;
        }else{
            col[node] = C;
        }
        bagaR(node, x);
        children[x][col[node]]++;
        sumR[x][col[node]] += rosii[node];
        if(children[x][C] == v[x].size()){
            col[x] = P;
        }else{
            col[x] = C;
        }
        bagaR(x, 0);
        Rerooting(x, node);
        children[x][col[node]]--;
        sumR[x][col[node]] -= rosii[node];
        col[x] = cx;
        bagaR(x, node);
        col[node] = cnode;
        children[node][col[x]]++;
        sumR[node][col[x]] += rosii[x];
        bagaR(node, 0);
    }
}

ll lgput(ll n, ll p){
    ll r = 1;
    while(p){
        if(p % 2){
            r *= n;
            r %= MOD;
        }
        n *= n;
        n %= MOD;
        p /= 2;
    }
    return r;
}

void add(ll &x, ll val){
    x += val;
    if(x >= MOD)
        x -= MOD;
    if(x < 0)
        x += MOD;
}

ll L[NMAX];

int main() {
    //ifstream cin(".in");
    //ofstream cout(".out");
    ios_base::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);
    ll n, d, i, criticalDif;
    cin >> n >> d;
    for(i = 1; i < n; i++){
        ll a, b;
        cin >> a >> b;
        v[a].push_back(b);
        v[b].push_back(a);
    }
    DFS(2, 0);
    Rerooting(2, 0);
    for(i = 1; i <= n; i++){
        if(adv[i] == P){
            add(criticalDif, -criticals[i]);
        }else{
            add(criticalDif, criticals[i]);
        }
    }
    ll B = criticalDif;
    ll A = (perdanti * n) % MOD * n % MOD;
    /// L0 = perdanti
    /// L1 = A + L0 * B
    /// Li = A + Li-1 * B
    L[0] = perdanti;
    for(i = 1; i <= d - 1; i++){
        L[i] = ((lgput(n, 2 * i) % MOD * perdanti) % MOD + (L[i - 1] * B) % MOD) % MOD;
    }
    ll schimba = (L[d - 1] * criticals[1]) % MOD;
    if(adv[1] == P){
        cout << schimba;
    }else{
        cout << (lgput(n, 2 * d) % MOD - schimba + MOD) % MOD;
    }
    return 0;
}

Compilation message (stderr)

startrek.cpp: In function 'void Rerooting(ll, ll)':
startrek.cpp:72:30: warning: comparison of integer expressions of different signedness: 'll' {aka 'long long int'} and 'std::vector<long long int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   72 |         if(children[node][C] == v[node].size() - 1){
      |            ~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~
startrek.cpp:80:27: warning: comparison of integer expressions of different signedness: 'll' {aka 'long long int'} and 'std::vector<long long int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   80 |         if(children[x][C] == v[x].size()){
      |            ~~~~~~~~~~~~~~~^~~~~~~~~~~~~~
startrek.cpp: In function 'int main()':
startrek.cpp:146:8: warning: unused variable 'A' [-Wunused-variable]
  146 |     ll A = (perdanti * n) % MOD * n % MOD;
      |        ^
startrek.cpp:152:70: warning: 'criticalDif' may be used uninitialized in this function [-Wmaybe-uninitialized]
  152 |         L[i] = ((lgput(n, 2 * i) % MOD * perdanti) % MOD + (L[i - 1] * B) % MOD) % MOD;
      |                                                            ~~~~~~~~~~^~~~

• Subtask 1: 0 / 0
• Subtask 2: 0 / 7
• Subtask 3: 8 / 8
• Subtask 4: 15 / 15
• Subtask 5: 15 / 15
• Subtask 6: 0 / 20
• Subtask 7: 0 / 20
• Subtask 8: 0 / 15