#include<bits/stdc++.h>
using namespace std;
using ll = long long;
const ll mod = 1000000007;
const int mx = 1500005;
bool valid[mx];
vector<int> graph[mx];
bool vis[mx];
int par[mx];
int dist[mx];
bool deg3[mx];
int n, k;
void dfs1(int cur, int par) {
for(int nxt : graph[cur]) if(nxt != par) {
dist[nxt] = dist[cur] + 1;
dfs1(nxt, cur);
}
for(int nxt : graph[cur]) if(nxt != par) {
dist[cur] = max(dist[cur], dist[nxt]);
}
}
void dfs2(int cur, int par) {
for(int nxt : graph[cur]) if(nxt != par) {
dist[nxt] = dist[cur] + 1;
dfs2(nxt, cur);
}
}
main() {
cin >> n >> k;
for(int i = 0; i < n - 1; i++) {
int s, d; cin >> s >> d;
graph[s].push_back(d);
graph[d].push_back(s);
}
vis[1] = true;
vector<int> q{1};
int qidx = 0;
while(qidx < q.size()) {
int cur = q[qidx++];
for(int nxt : graph[cur]) {
if(!vis[nxt]) {
q.push_back(nxt);
vis[nxt] = true;
}
}
}
int far = q.back();
memset(vis, false, sizeof(vis));
vis[far] = true;
q = {far};
qidx = 0;
while(qidx < q.size()) {
int cur = q[qidx++];
for(int nxt : graph[cur]) {
if(!vis[nxt]) {
vis[nxt] = true;
par[nxt] = cur;
dist[nxt] = dist[cur] + 1;
q.push_back(nxt);
}
}
}
int far2 = q.back();
int width = dist[far2] + 1;
int rad;
if(width % 2 == 0) {
rad = width / 2;
int centre1 = far2;
for(int i = 0; i < rad - 1; i++) {
centre1 = par[centre1];
}
int centre2 = par[centre1];
dist[centre1] = 0;
dist[centre2] = 0;
dfs1(centre1, centre2);
dfs1(centre2, centre1);
rad++;
} else {
rad = width / 2;
int centre = far2;
for(int i = 0; i < rad; i++) {
centre = par[centre];
}
dist[centre] = 0;
dfs1(centre, 0);
}
ll mul = 1;
for(int i = 1; i <= n; i++) {
if(dist[i] + rad + 1 < k) {
mul += mul;
if(mul >= mod) mul -= mod;
} else {
valid[i] = true;
}
}
int root = -1;
for(int i = 1; i <= n; i++) {
if(valid[i]) {
root = i;
}
}
if(root == -1) {
cout << "YES" << endl;
cout << mul << endl;
return 0;
}
bool is_line = true;
for(int i = 1; i <= n; i++) if(valid[i]) {
int deg = 0;
for(int nxt : graph[i]) if(valid[nxt]) deg++;
if(deg >= 3) {
deg3[i] = true;
is_line = false;
root = i;
}
}
if(is_line) {
cout << "YES" << endl;
ll ans = (mul * k) % mod;
cout << ans << endl;
return 0;
}
dist[root] = 0;
dfs2(root, 0);
for(int i = 1; i <= n; i++) if(valid[i] && deg3[i]) {
if(k & 1) {
if(dist[i] % k != 0) {
cout << "NO" << endl << 0 << endl;
return 0;
}
} else {
if(dist[i] % (k / 2) != 0) {
cout << "NO" << endl << 0 << endl;
return 0;
}
}
}
mul += mul;
mul %= mod;
cout << "YES" << endl << mul << endl;
}
Compilation message
wells.cpp:28:1: warning: ISO C++ forbids declaration of 'main' with no type [-Wreturn-type]
28 | main() {
| ^~~~
wells.cpp: In function 'int main()':
wells.cpp:38:13: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
38 | while(qidx < q.size()) {
| ~~~~~^~~~~~~~~~
wells.cpp:52:13: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
52 | while(qidx < q.size()) {
| ~~~~~^~~~~~~~~~
| # |
결과 |
실행 시간 |
메모리 |
Grader output |
| 1 |
Correct |
20 ms |
36980 KB |
Output is correct |
| 2 |
Incorrect |
19 ms |
36948 KB |
Output isn't correct |
| 3 |
Halted |
0 ms |
0 KB |
- |
| # |
결과 |
실행 시간 |
메모리 |
Grader output |
| 1 |
Correct |
20 ms |
36980 KB |
Output is correct |
| 2 |
Incorrect |
19 ms |
36948 KB |
Output isn't correct |
| 3 |
Halted |
0 ms |
0 KB |
- |
| # |
결과 |
실행 시간 |
메모리 |
Grader output |
| 1 |
Correct |
20 ms |
36980 KB |
Output is correct |
| 2 |
Incorrect |
19 ms |
36948 KB |
Output isn't correct |
| 3 |
Halted |
0 ms |
0 KB |
- |
| # |
결과 |
실행 시간 |
메모리 |
Grader output |
| 1 |
Correct |
20 ms |
36980 KB |
Output is correct |
| 2 |
Incorrect |
19 ms |
36948 KB |
Output isn't correct |
| 3 |
Halted |
0 ms |
0 KB |
- |
