This submission is migrated from previous version of oj.uz, which used different machine for grading. This submission may have different result if resubmitted.
#include <bits/stdc++.h>
#pragma GCC target ("avx2")
#pragma GCC optimization ("O3")
#pragma GCC optimization ("unroll-loops")
using namespace std;
const int N = 5e4 + 10;
const int mod = 1e9 + 7;
const int base = 29;
int n, ti;
char c[N];
int big[N], sz[N], del[N];
vector <int> g[N];
void dfs(int u, int p) {
big[u] = 0, sz[u] = 1;
for (auto v: g[u]) {
if (v == p || del[v] == ti) continue;
dfs(v, u);
sz[u] += sz[v];
if (sz[v] > sz[big[u]]) big[u] = v;
}
}
int centroid(int u) {
int num = sz[u] / 2;
while (sz[big[u]] > num) u = big[u];
return u;
}
int H[N], power[N];
int rH[N];
int get_hash(int L, int R) {
return (0LL + H[R] - 1LL * H[L - 1] * power[R - L + 1] + 1LL * mod * mod) % mod;
}
int check(int u, int len) {
dfs(u, 0);
u = centroid(u);
del[u] = ti;
H[1] = c[u] - 'a' + 1;
unordered_set <int> s;
function <void(int, int, int)> add = [&](int u, int p, int d) {
if (d * 2 > len + 3) return;
H[d] = (1LL * H[d - 1] * base + c[u] - 'a' + 1) % mod;
s.insert(H[d]);
for (auto v: g[u]) {
if (v == p || del[v] == ti) continue;
add(v, u, d + 1);
}
};
rH[1] = c[u] - 'a' + 1;
s.insert(H[1]);
int ok = 0;
function <void(int, int, int)> calc = [&](int u, int p, int d) {
if (d > len || ok) return;
H[d] = (1LL * H[d - 1] * base + c[u] - 'a' + 1) % mod;
int rem = len - d + 1;
rH[d] = (1LL * power[d - 1] * (c[u] - 'a' + 1) + rH[d - 1]) % mod;
if (d * 2 - len > 0 && rH[d * 2 - len] == H[d * 2 - len]) {
if (s.find(get_hash(d * 2 - len, d)) != s.end()) {
ok = 1;
return;
}
}
for (auto v: g[u]) {
if (v == p || del[v] == ti) continue;
calc(v, u, d + 1);
}
};
for (auto v: g[u]) {
if (del[v] == ti) continue;
calc(v, u, 2);
if (ok) return 1;
add(v, u, 2);
}
s.clear();
reverse(g[u].begin(), g[u].end());
for (auto v: g[u]) {
if (del[v] == ti) continue;
calc(v, u, 2);
if (ok) return 1;
add(v, u, 2);
}
for (auto v: g[u]) {
if (del[v] == ti) continue;
if (check(v, len)) return 1;
}
return 0;
}
int main() {
ios :: sync_with_stdio(0); cin.tie(0);
cin >> n;
for (int i = 1; i <= n; ++i) cin >> c[i];
power[0] = 1;
for (int i = 1; i <= n; ++i) power[i] = 1LL * power[i - 1] * base % mod;
for (int i = 1; i < n; ++i) {
int u, v;
cin >> u >> v;
g[u].push_back(v);
g[v].push_back(u);
}
int ans = 0;
int L = 0, R = n / 2;
while (R - L > 1) {
int mid = L + R >> 1;
++ti;
if (check(1, mid * 2)) L = mid;
else R = mid;
}
++ti;
if (check(1, R * 2)) ans = R * 2;
else ans = L * 2;
if (!ans) ans = 1;
L = 1, R = n / 2 + 1;
while (R - L > 1) {
int mid = L + R >> 1;
++ti;
if (check(1, mid * 2 - 1)) L = mid;
else R = mid;
}
++ti;
if (check(1, R * 2 - 1)) ans = max(ans, R * 2 - 1);
else ans = max(ans, L * 2 - 1);
cout << ans;
}
Compilation message (stderr)
lampice.cpp:3: warning: ignoring '#pragma GCC optimization' [-Wunknown-pragmas]
3 | #pragma GCC optimization ("O3")
|
lampice.cpp:4: warning: ignoring '#pragma GCC optimization' [-Wunknown-pragmas]
4 | #pragma GCC optimization ("unroll-loops")
|
lampice.cpp: In lambda function:
lampice.cpp:61:13: warning: unused variable 'rem' [-Wunused-variable]
61 | int rem = len - d + 1;
| ^~~
lampice.cpp: In function 'int main()':
lampice.cpp:110:21: warning: suggest parentheses around '+' inside '>>' [-Wparentheses]
110 | int mid = L + R >> 1;
| ~~^~~
lampice.cpp:121:21: warning: suggest parentheses around '+' inside '>>' [-Wparentheses]
121 | int mid = L + R >> 1;
| ~~^~~
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