// Om Namah Shivaya
// GM in 109 days
#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace std;
using namespace __gnu_pbds;
template <class T> using Tree = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
typedef long long int ll;
typedef long double ld;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
#define fastio ios_base::sync_with_stdio(false); cin.tie(NULL)
#define endl '\n'
#define pb push_back
#define conts continue
#define all(a) a.begin(), a.end()
#define rall(a) a.rbegin(), a.rend()
#define yes cout << "YES" << endl
#define no cout << "NO" << endl
#define ff first
#define ss second
#define ceil2(x,y) ((x+y-1) / (y))
#define sz(a) a.size()
#define setbits(x) __builtin_popcountll(x)
#ifndef ONLINE_JUDGE
#define debug(x) cout << #x <<" = "; print(x); cout << endl
#else
#define debug(x)
#endif
#define rep(i,n) for(int i = 0; i < n; ++i)
#define rep1(i,n) for(int i = 1; i <= n; ++i)
#define rev(i,s,e) for(int i = s; i >= e; --i)
#define trav(i,a) for(auto &i : a)
bool iseven(ll n) {if ((n & 1) == 0) return true; return false;}
void print(ll t) {cout << t;}
void print(int t) {cout << t;}
void print(string t) {cout << t;}
void print(char t) {cout << t;}
void print(double t) {cout << t;}
void print(ld t) {cout << t;}
template <class T, class V> void print(pair <T, V> p);
template <class T> void print(vector <T> v);
template <class T> void print(set <T> v);
template <class T, class V> void print(map <T, V> v);
template <class T> void print(multiset <T> v);
template <class T, class V> void print(pair <T, V> p) {cout << "{"; print(p.ff); cout << ","; print(p.ss); cout << "}";}
template <class T> void print(vector <T> v) {cout << "[ "; for (T i : v) {print(i); cout << " ";} cout << "]";}
template <class T> void print(set <T> v) {cout << "[ "; for (T i : v) {print(i); cout << " ";} cout << "]";}
template <class T> void print(multiset <T> v) {cout << "[ "; for (T i : v) {print(i); cout << " ";} cout << "]";}
template <class T, class V> void print(map <T, V> v) {cout << "[ "; for (auto i : v) {print(i); cout << " ";} cout << "]";}
template<typename T> void amin(T &a, T b) { a = min(a, b); }
template<typename T> void amax(T &a, T b) { a = max(a, b); }
void usaco(string filename) {
freopen((filename + ".in").c_str(), "r", stdin);
freopen((filename + ".out").c_str(), "w", stdout);
}
const int MOD = 1e9 + 7;
const int maxn = 3e5 + 5;
const int inf1 = 1e9 + 5;
const ll inf2 = ll(1e18) + 5;
vector<int> adj[maxn], col(maxn), depth(maxn), mndepth(maxn, inf1);
vector<pii> adj2[maxn];
vector<bool> vis(maxn);
struct lca_algo {
// LCA template (for graphs with 1-based indexing)
int LOG = 1;
vector<int> depth;
vector<vector<int>> up;
lca_algo() {
}
lca_algo(int n) {
lca_init(n);
}
void lca_init(int n) {
while ((1 << LOG) < n) LOG++;
up = vector<vector<int>>(n + 1, vector<int>(LOG, 1));
depth = vector<int>(n + 1);
lca_dfs(1, -1);
}
void lca_dfs(int node, int par) {
trav(child, adj[node]) {
if (child == par) conts;
up[child][0] = node;
rep1(j, LOG - 1) {
up[child][j] = up[up[child][j - 1]][j - 1];
}
depth[child] = depth[node] + 1;
lca_dfs(child, node);
}
}
int lift(int u, int k) {
rep(j, LOG) {
if (k & (1 << j)) {
u = up[u][j];
}
}
return u;
}
int query(int u, int v) {
if (depth[u] < depth[v]) swap(u, v);
int k = depth[u] - depth[v];
u = lift(u, k);
if (u == v) return u;
rev(j, LOG - 1, 0) {
if (up[u][j] != up[v][j]) {
u = up[u][j];
v = up[v][j];
}
}
u = up[u][0];
return u;
}
};
void dfs1(int node, int par) {
trav(child, adj[node]) {
if (child == par) conts;
depth[child] = depth[node] + 1;
dfs1(child, node);
}
}
void build(int node, int par) {
trav(child, adj[node]) {
if (child == par) conts;
build(child, node);
amin(mndepth[node], mndepth[child]);
// will this edge be painted blue? (i.e) is it necessary for nodes 'node' and 'child' to have the same color?
// if it is, then one of the m paths must pass through the given edge
// a path passes through this edge only if the minimum depth node reachable by 'child' is lesser than the depth of 'node' (same logic as finding bridges in a graph, where we minimize the low time for each node and check if the current edge is a bridge)
if (mndepth[child] < depth[node]) {
adj2[node].pb({child, 0});
adj2[child].pb({node, 0});
}
}
}
bool flag;
void dfs2(int node) {
vis[node] = 1;
for (auto [child, w] : adj2[node]) {
if (vis[child]) {
if ((col[node] ^ w) != col[child]) {
flag = false;
}
}
else {
col[child] = col[node] ^ w;
dfs2(child);
}
}
}
void solve(int test_case)
{
// editorial approach: https://hsin.hr/coci/archive/2017_2018/
int n, m; cin >> n >> m;
rep1(i, n - 1) {
int u, v; cin >> u >> v;
adj[u].pb(v), adj[v].pb(u);
}
lca_algo LCA(n);
depth[1] = 0;
dfs1(1, -1);
while (m--) {
int u, v; cin >> u >> v;
int lca = LCA.query(u, v);
amin(mndepth[u], depth[lca]);
amin(mndepth[v], depth[lca]);
if (lca != u and lca != v) {
adj2[u].pb({v, 1});
adj2[v].pb({u, 1});
}
}
build(1, -1);
int ans = 1;
for (int i = 2; i <= n; ++i) {
if (vis[i]) conts;
flag = true;
dfs2(i);
if (!flag) {
cout << 0 << endl;
return;
}
ans = (ans * 2) % MOD;
}
cout << ans << endl;
}
int main()
{
fastio;
int t = 1;
// cin >> t;
rep1(i, t) {
solve(i);
}
return 0;
}
Compilation message
usmjeri.cpp: In function 'void usaco(std::string)':
usmjeri.cpp:64:12: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
64 | freopen((filename + ".in").c_str(), "r", stdin);
| ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
usmjeri.cpp:65:12: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
65 | freopen((filename + ".out").c_str(), "w", stdout);
| ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
| # |
Verdict |
Execution time |
Memory |
Grader output |
| 1 |
Correct |
117 ms |
40456 KB |
Output is correct |
| # |
Verdict |
Execution time |
Memory |
Grader output |
| 1 |
Correct |
318 ms |
88312 KB |
Output is correct |
| # |
Verdict |
Execution time |
Memory |
Grader output |
| 1 |
Correct |
9 ms |
18004 KB |
Output is correct |
| 2 |
Correct |
10 ms |
18380 KB |
Output is correct |
| # |
Verdict |
Execution time |
Memory |
Grader output |
| 1 |
Correct |
11 ms |
18004 KB |
Output is correct |
| 2 |
Correct |
10 ms |
18232 KB |
Output is correct |
| # |
Verdict |
Execution time |
Memory |
Grader output |
| 1 |
Correct |
13 ms |
18644 KB |
Output is correct |
| 2 |
Correct |
13 ms |
18584 KB |
Output is correct |
| # |
Verdict |
Execution time |
Memory |
Grader output |
| 1 |
Correct |
18 ms |
18592 KB |
Output is correct |
| 2 |
Correct |
13 ms |
18688 KB |
Output is correct |
| # |
Verdict |
Execution time |
Memory |
Grader output |
| 1 |
Correct |
465 ms |
67212 KB |
Output is correct |
| 2 |
Correct |
488 ms |
69236 KB |
Output is correct |
| 3 |
Correct |
272 ms |
50216 KB |
Output is correct |
| # |
Verdict |
Execution time |
Memory |
Grader output |
| 1 |
Correct |
549 ms |
71320 KB |
Output is correct |
| 2 |
Correct |
548 ms |
71384 KB |
Output is correct |
| 3 |
Correct |
329 ms |
52612 KB |
Output is correct |
| # |
Verdict |
Execution time |
Memory |
Grader output |
| 1 |
Correct |
543 ms |
71820 KB |
Output is correct |
| 2 |
Correct |
538 ms |
68292 KB |
Output is correct |
| 3 |
Correct |
330 ms |
53592 KB |
Output is correct |
| # |
Verdict |
Execution time |
Memory |
Grader output |
| 1 |
Correct |
565 ms |
72208 KB |
Output is correct |
| 2 |
Correct |
540 ms |
72740 KB |
Output is correct |
| 3 |
Correct |
308 ms |
50896 KB |
Output is correct |
