#include <bits/stdc++.h>
using namespace std;
#define task ""
#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()
const int MOD = 1e9 + 7;
const int MAX = 50005;
const int BASE = 256;
int n;
int len;
char cc;
int maxH;
int sz[MAX];
char a[MAX];
int pw[MAX];
bool rem[MAX];
vector<int> adj[MAX];
unordered_map<int, bool> mp[MAX];
int dfsSZ(int u, int p) {
sz[u] = 1;
for (int v: adj[u]) if (v != p && !rem[v]) {
sz[u] += dfsSZ(v, u);
}
return sz[u];
}
int findCentroid(int u, int p, int n) {
for (int v: adj[u]) if (v != p && !rem[v]) {
if ((sz[v] << 1) > n)
return findCentroid(v, u, n);
}
return u;
}
void dfs(int u, int p, bool upd, int h, int up, int dw, bool &found) {
up = (1LL * up * BASE + (a[u] - 'a' + 1)) % MOD; dw = (dw + 1LL * pw[h - 1] * (a[u] - 'a' + 1)) % MOD;
int value = (1LL * pw[len - h] * dw - up + MOD) % MOD;
if (upd) mp[h][value] = true;
else {
if (h + 1 == len && (1LL * dw * BASE + (cc - 'a' + 1)) % MOD == up) {
found = true;
return;
}
if (len > h && mp[len - h - 1].find(value) != mp[len - h - 1].end()) {
found = true;
return;
}
}
if (h < len) {
for (int v: adj[u]) if (v != p && !rem[v]) {
dfs(v, u, upd, h + 1, up, dw, found);
maxH = max(maxH, h + 1);
if (found) return;
}
}
}
void solve(int u,bool &found) {
int c = findCentroid(u, p, dfsSZ(u, p)); rem[c] = true;
maxH = 1;
cc = a[c];
for (int v: adj[c]) if (!rem[v]) {
dfs(v, c, 0, 1, a[c] - 'a' + 1, 0, found);
if (found) return;
dfs(v, c, 1, 1, a[c] - 'a' + 1, 0, found);
}
for (int i = 0; i <= maxH; ++i) {
mp[i].clear();
}
for (int v: adj[c]) if (!rem[v]) {
solve(v,found);
if (found) return;
}
}
bool ok(int x) {
for (int i = 0; i <= n; ++i) mp[i].clear();
memset(rem, false, sizeof rem);
bool found = false; len = x;
solve(1, found);
return found;
}
int main() {
ios_base::sync_with_stdio(false); cin.tie(nullptr);
if (fopen(task".inp", "r")) {
freopen(task".inp", "r", stdin);
freopen(task".out", "w", stdout);
}
cin >> n;
cin >> (a + 1);
for (int i = 1; i < n; ++i) {
int u, v; cin >> u >> v;
adj[u].push_back(v);
adj[v].push_back(u);
}
pw[0] = 1; for (int i = 1; i <= n; ++i) {
pw[i] = 1LL * pw[i - 1] * BASE % MOD;
}
int ans = 1;
for (int i = 0; i < 2; ++i) {
int l = 0, r = n / 2 + 1;
while (r - l > 1) {
int mid = l + r >> 1;
if (ok(i + 2 * mid)) l = mid; else r = mid;
}
ans = max(ans, i + 2 * l);
}
cout << ans;
return 0;
}
Compilation message
lampice.cpp: In function 'void solve(int, bool&)':
lampice.cpp:61:29: error: 'p' was not declared in this scope
61 | int c = findCentroid(u, p, dfsSZ(u, p)); rem[c] = true;
| ^
lampice.cpp: In function 'int main()':
lampice.cpp:110:25: warning: suggest parentheses around '+' inside '>>' [-Wparentheses]
110 | int mid = l + r >> 1;
| ~~^~~
lampice.cpp:92:10: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
92 | freopen(task".inp", "r", stdin);
| ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~
lampice.cpp:93:10: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
93 | freopen(task".out", "w", stdout);
| ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~
