Submission #577687

#	Time	Username	Problem	Language	Result	Execution time	Memory
577687		talant117408	Star Trek (CEOI20_startrek)	C++17	Compilation error	0 ms	0 KiB

startrek

#include <bits/stdc++.h>
 
using namespace std;
 
typedef long long ll;
typedef pair <int, int> pii;
typedef pair <ll, ll> pll;

#define long                unsigned long 
#define pb                  push_back
#define mp                  make_pair
#define all(v)              (v).begin(),(v).end()
#define rall(v)             (v).rbegin(),(v).rend()
#define lb                  lower_bound
#define ub                  upper_bound
#define sz(v)               int((v).size())
#define do_not_disturb      ios::sync_with_stdio(0);cin.tie(0);cout.tie(0);
#define endl                '\n'

const int mod = 1e9+7;

ll add(ll a, ll b) {
    return ((a + b) % mod + mod) % mod;
}

ll mult(ll a, ll b) {
    return ((a * b) % mod + mod) % mod;
}

ll binpow(ll a, ll b) {
    ll res = 1;
    while (b) {
        if (b&1) res = mult(res, a);
        a = mult(a, a);
        b >>= 1;
    }
    return res;
}

const int N = 1e5+7;
vector <int> graph[N];
int state[N], state_root[N], losing_children[N], parent[N], life_changing[N];
int losing[N], winning[N];

int dfs(int v, int p) {
    parent[v] = p;
    int l = 0;
    for (auto to : graph[v]) {
        if (to == parent[v]) {
            continue;
        }
        l += dfs(to, v);
    }
    losing_children[v] = l;
    state[v] = 1 - (losing_children[v] > 0);
    return state[v];
}

void dfs2(int v, int i) {
    state_root[v] = state[v];
    (state[v] ? losing[i] : winning[i])++;
    for (auto to : graph[v]) {
        if (to == parent[v]) {
            continue;
        }
        if (state[to] && !state[v] && !state[parent[v]] && losing_children[v] == 1) {
            losing_children[v]--;
            losing_children[to]++;
            state[v] = 1;
            state[to] = 0;
            dfs2(to, i);
            losing_children[v]++;
            losing_children[to]--;
            state[v] = 0;
            state[to] = 1;
        }
        else {
            dfs2(to, i);
        }
    }
}

void dfs3(int v, int i, bool flag = 1) {
    if (state[v] && !state[parent[v]] && losing_children[parent[v]] > 1) {
        flag = 0;
    }
    if (state[v] && flag) {
        life_changing[i]++;
    }
    for (auto to : graph[v]) {
        if (to == parent[v]) {
            continue;
        }
        dfs3(to, i, flag);
    }
}

void solve() {
    int n;
    ll D;
    cin >> n >> D;
    for (int i = 1; i < n; i++) {
        int a, b;
        cin >> a >> b;
        graph[a].pb(b);
        graph[b].pb(a);
    }
    if (n == 2) {
        cout << binpow(2, D*2) << endl;
    }
    else if (D <= 1e5) {
        ll all_life_changing = 0;
        dfs(1, 1);
        dfs2(1, D);
        for (int i = 1; i <= n; i++) {
            dfs(i, i);
            dfs3(i, i);
            all_life_changing = add(all_life_changing, (state_root[i] ? 1 : -1) * life_changing[i]);
        }
        for (int j = D-1; j >= 1; j--) {
            losing[j] = add(losing[j], mult(add(mult(n, n), -all_life_changing), losing[j+1])); 
            winning[j] = add(binpow(n, D-j+2), -losing[j]);
        }
        if (state_root[1]) {
            cout << mult(life_changing[1], losing[1]);
        }
        else {
            cout << add(mult(n, winning[1]), mult(n-life_changing[1], losing[1]));
        }
    }
}

int main() {
    do_not_disturb
    
    int t = 1;
    //~ cin >> t;
    while (t--) {
        solve();
    }
    
    return 0;
}
/*
13 1
13 1
1 2
1 3
1 4
1 5
5 6
1 12
12 13
1 7
7 8
8 11
8 9
10 9
*/

Compilation message (stderr)

startrek.cpp:108:2: error: extended character   is not valid in an identifier
  108 |     if (n == 2) {
      |  ^
startrek.cpp:108:5: error: extended character   is not valid in an identifier
  108 |     if (n == 2) {
      |    ^
startrek.cpp: In function 'void solve()':
startrek.cpp:108:2: error: '\U000000a0' was not declared in this scope
  108 |     if (n == 2) {
      |  ^
startrek.cpp:111:5: error: 'else' without a previous 'if'
  111 |     else if (D <= 1e5) {
      |     ^~~~