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| #include <bits/stdc++.h>
using namespace std;
using LL = long long;
#define FOR(i, x, y) for (decay<decltype(y)>::type i = (x), _##i = (y); i < _##i; ++i)
#define FORD(i, x, y) for (decay<decltype(x)>::type i = (x), _##i = (y); i > _##i; --i)
#ifdef zerol
#define dbg(args...) do { cout << "\033[32;1m" << #args << " -> "; err(args); } while (0)
#else
#define dbg(...)
#endif
void err() { cout << "\033[39;0m" << endl; }
template<template<typename...> class T, typename t, typename... Args>
void err(T<t> a, Args... args) { for (auto x: a) cout << x << ' '; err(args...); }
template<typename T, typename... Args>
void err(T a, Args... args) { cout << a << ' '; err(args...); }
// -----------------------------------------------------------------------------
const int maxn = 1E5 * 4 + 100;
namespace sam {
const int M = maxn;
int t[M][26], len[M] = {-1}, fa[M], sz, last;
int ml[M], ml_fr[M];
int c[M] = {1}, a[M];
bool cnt[M][2];
int pos[M][2], one[M][2];
vector<int> G[M];
void init() {
FOR (i, 1, sz) {
memset(t[i], 0, sizeof t[0]);
memset(cnt[i], 0, sizeof cnt[0]);
memset(pos[i], -1, sizeof pos[0]);
memset(one[i], -1, sizeof one[0]);
ml[i] = c[i] = a[i] = 0;
G[i].clear();
}
sz = 2; last = 1;
}
void re() { last = 1; }
void ins(int ch, int id, int pp) {
int p = last, np = 0, nq = 0, q = -1;
if (!t[p][ch]) {
np = sz++;
len[np] = len[p] + 1;
for (; p && !t[p][ch]; p = fa[p]) t[p][ch] = np;
}
if (!p) fa[np] = 1;
else {
q = t[p][ch];
if (len[p] + 1 == len[q]) fa[np] = q;
else {
nq = sz++; len[nq] = len[p] + 1;
memcpy(t[nq], t[q], sizeof t[0]);
memcpy(one[nq], one[q], sizeof t[0]);
fa[nq] = fa[q];
fa[np] = fa[q] = nq;
for (; t[p][ch] == q; p = fa[p]) t[p][ch] = nq;
}
}
last = np ? np : nq ? nq : q;
cnt[last][id] = 1; pos[last][id] = pp;
}
void rsort() {
FOR (i, 1, sz) c[len[i]]++;
FOR (i, 1, sz) c[i] += c[i - 1];
FOR (i, 1, sz) a[--c[len[i]]] = i;
}
void build() {
FOR (i, 2, sz) G[fa[i]].push_back(i);
}
}
namespace pam {
const int M = maxn;
int t[M][26], fa[M], len[M], rs[M];
int sz, n, last;
int N(int l) {
memset(t[sz], 0, sizeof t[0]);
len[sz] = l;
return sz++;
}
void init() {
rs[n = sz = 0] = -1;
last = N(0);
fa[last] = N(-1);
}
int get_fa(int p) {
while (rs[n - 1 - len[p]] != rs[n]) p = fa[p];
return p;
}
void ins(int ch) {
rs[++n] = ch;
int p = get_fa(last);
if (!t[p][ch]) {
int np = N(len[p] + 2);
fa[np] = t[get_fa(fa[p])][ch];
t[p][ch] = np;
}
last = t[p][ch];
}
}
void add(string& s, char* a, char* b, int la, int ra, int lb, int rb) {
s.clear();
FOR (i, lb, rb) s += b[i];
FOR (i, la, ra) s += a[i];
}
int pa_ml[maxn], pa_ml_fr[maxn];
string go(char* a, char* b) {
sam::init();
int la = strlen(a), lb = strlen(b);
FORD (i, la - 1, -1) sam::ins(a[i] - 'a', 0, i);
sam::re();
FOR (i, 0, lb) sam::ins(b[i] - 'a', 1, i);
sam::cnt[1][1] = 1;
sam::rsort(); sam::build();
{
using namespace sam;
FORD (i, sz - 1, 1) {
int u = sam::a[i];
if (cnt[u][1]) {
cnt[fa[u]][1] |= cnt[u][1];
pos[fa[u]][1] = pos[u][1];
}
}
FOR (i, 1, sz) {
int u = sam::a[i];
if (cnt[u][1]) ml[u] = len[u], ml_fr[u] = pos[u][1];
for (int& v: G[u]) ml[v] = ml[u], ml_fr[v] = ml_fr[u];
}
FOR (i, 1, sz)
if (pos[i][0] != -1) {
pa_ml[pos[i][0]] = ml[i];
pa_ml_fr[pos[i][0]] = ml_fr[i];
}
}
pam::init();
int ans = 0, al = -1, ar = -1, bl = -1, br = -1;
string last, nxt;
pa_ml[la] = 0;
FOR (i, -1, la) {
pam::ins(a[i] - 'a');
int pl = i >= 0 ? pam::len[pam::last] : 0; // notice!
int pl2 = pa_ml[i + 1];
int cur = pl + pl2 * 2;
if (pl2 && cur >= ans) {
if (cur == ans) add(last, a, b, al, ar, bl, br);
int arr = i + 1 + pl2, all = arr - pl - pl2;
int brr = pa_ml_fr[i + 1] + 1, bll = brr - pl2;
if (cur == ans) {
add(nxt, a, b, all, arr, bll, brr);
if (last < nxt) continue;
}
ans = cur;
al = all; ar = arr; bl = bll; br = brr;
}
}
add(last, a, b, al, ar, bl, br);
return last;
}
char a[maxn], b[maxn];
int main() {
int T; cin >> T;
memset(sam::pos, -1, sizeof sam::pos);
memset(sam::one, -1, sizeof sam::one);
while (T--) {
scanf("%s%s", a, b);
auto ans1 = go(b, a);
reverse(a, a + strlen(a));
reverse(b, b + strlen(b));
auto ans2 = go(a, b);
string ans = ans1;
if (ans.length() < ans2.length() ||
(ans.length() == ans2.length() && ans > ans2)) ans = ans2;
cout << (ans.empty() ? "-1" : ans) << endl;
}
}
|