#define ATCODER #define _USE_MATH_DEFINES #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include using namespace std; using ll = long long; using ld = long double; using pll = pair; using pdd = pair; #define FOR(i, a, b) for (ll i = (a); i < (b); i++) #define REP(i, n) for (ll i = 0; i < (n); i++) #define ROF(i, a, b) for (ll i = (b - 1); i >= (a); i--) #define PER(i, n) for (ll i = n - 1; i >= 0; i--) #define VL vector #define VVL vector> #define VP vector> #define LPQ(T) priority_queue, greater> #define all(i) begin(i), end(i) #define SORT(i) sort(all(i)) #define EXISTBIT(x, i) (((x >> i) & 1) != 0) #define CHMAX(n, v) n = n < v ? v : n #define CHMIN(n, v) n = n > v ? v : n #define MP(a, b) make_pair(a, b) #define DET2(x1, y1, x2, y2) (x1) * (y2) - (x2) * (y1) #define DET3(x1, y1, z1, x2, y2, z2, x3, y3, z3) (x1) * (y2) * (z3) + (x2) * (y3) * (z1) + (x3) * (y1) * (z2) - (z1) * (y2) * (x3) - (z2) * (y3) * (x1) - (z3) * (y1) * (x2) #define INC(a) \ for (auto &v : a) \ v++; #define DEC(a) \ for (auto &v : a) \ v--; #define SQU(x) (x) * (x) #ifdef ATCODER #include using namespace atcoder; using mint = modint1000000007; using mint2 = modint998244353; #endif template vector read(size_t n) { vector ts(n); for (size_t i = 0; i < n; i++) cin >> ts[i]; return ts; } template void read_tuple_impl(TV &) {} template void read_tuple_impl(TV &ts) { get(ts).emplace_back(*(istream_iterator(cin))); read_tuple_impl(ts); } template decltype(auto) read_tuple(size_t n) { tuple...> ts; for (size_t i = 0; i < n; i++) read_tuple_impl(ts); return ts; } using val = mint; using val2 = mint2; using func = ll; val op(val a, val b) { return a*b; } val e() { return 1; } val2 op2(val2 a, val2 b) { return a*b; } val2 e2() { return 1; } val mp(func f, val a) { return a + f; } func comp(func f, func g) { return f + g; } func id() { return 0; } ll di[4] = {1, 0, -1, 0}; ll dj[4] = {0, 1, 0, -1}; ll si[4] = {0, 3, 3, 0}; ll sj[4] = {0, 0, 3, 3}; // ll di[4] = { -1,-1,1,1 }; // ll dj[4] = { -1,1,-1,1 }; ll di8[8] = {0, -1, -1, -1, 0, 1, 1, 1}; ll dj8[8] = {-1, -1, 0, 1, 1, 1, 0, -1}; struct PalindromicTree { // // private: struct node { map link; int suffix_link; ll len; ll count; }; vector c; string s; int active_idx; node* create_node() { c.emplace_back(); node* ret = &c.back(); ret->count = 0; return ret; } // this->s の状態に依存する int find_prev_palindrome_idx(int node_id) { const int pos = int(s.size()) - 1; while (true) { const int opposite_side_idx = pos - 1 - c[node_id].len; if (opposite_side_idx >= 0 && s[opposite_side_idx] == s.back()) break; node_id = c[node_id].suffix_link; // 次の回文に移動 } return node_id; } bool debug_id2string_dfs(int v, int id, vector& charas) { if (v == id) return true; for (auto kv : c[v].link) { if (debug_id2string_dfs(kv.second, id, charas)) { charas.push_back(kv.first); return true; } } return false; } public: PalindromicTree() { node* size_m1 = create_node(); // 長さ-1のノードを作成 size_m1->suffix_link = 0; // -1 の親suffixは自分自身 size_m1->len = -1; node* size_0 = create_node(); // 長さ0のノードを作成 size_0->suffix_link = 0; // 親は長さ-1のノード size_0->len = 0; active_idx = 0; } int get_active_idx() const { return active_idx; } node* get_node(int id) { return &c[id]; } void add(char ch) { s.push_back(ch); // ch + [A] + ch が回文となるものを探す const int a = find_prev_palindrome_idx(active_idx); //新しいノードへのリンクが発生するか試す const auto inserted_result = c[a].link.insert(make_pair(ch, int(c.size()))); active_idx = inserted_result.first->second; // insertの成否に関わらず、iteratorが指す先は新しい回文のindex if (!inserted_result.second) { c[active_idx].count++; // その回文が現れた回数が増加 return; // 既にリンクが存在したので、新しいノードを作る必要がない } // 実際に新しいノードを作成 node* nnode = create_node(); nnode->count = 1; nnode->len = c[a].len + 2; // ch + [A] + ch だから、長さは len(A) + 2 // suffix_linkの設定 if (nnode->len == 1) { // この時だけsuffix_linkはsize 0に伸ばす nnode->suffix_link = 1; } else { // ch + [B] + ch が回文になるものを探す。ただし長さはaより小さいもの const int b = find_prev_palindrome_idx(c[a].suffix_link); nnode->suffix_link = c[b].link[ch]; } } //各文字列が何回現れるか計算する // O(n) vector build_frequency() { vector frequency(c.size()); //常に親ノードのid < 子ノードのidが成り立つので、idを大きい順から回せばよい for (int i = int(c.size()) - 1; i > 0; i--) { frequency[i] += c[i].count; frequency[c[i].suffix_link] += frequency[i]; } return frequency; } }; void solve() { ll n,m; cin>>n>>m; string s; cin>>s; PalindromicTree pt1,pt2; vector pal(n+1),rpal(n+1); pal[0]=true; rpal[n]=true; REP(i,n){ pt1.add(s[i]); if(pt1.get_node(pt1.active_idx)->len==i+1){ pal[i+1]=true; } } PER(i,n){ pt2.add(s[i]); if(pt2.get_node(pt2.active_idx)->len==n-i){ rpal[i]=true; } } ll ans=1e18; REP(i,n){ if(pal[i]&&rpal[i]){ ll tmp=m/n - 1; ll le=tmp*n; while(le=m || le+n-i>=m){ CHMIN(ans,tmp+1); break; } le+=n; tmp++; } } } if(ans>1e17)ans=-1; cout<> t; while (t--) { solve(); } return 0; }