| #include <iostream> |
| #include <string> |
| #include <vector> |
| #include <algorithm> |
|
|
| using namespace std; |
|
|
| struct SuffixArray { |
| int n; |
| string s; |
| vector<int> sa, rank, lcp; |
| vector<vector<int>> st; |
| vector<int> lg; |
|
|
| SuffixArray() {} |
|
|
| void init(const string& str) { |
| s = str; |
| n = s.length(); |
| sa.resize(n); |
| rank.resize(n); |
| lcp.resize(n); |
|
|
| for (int i = 0; i < n; i++) { |
| sa[i] = i; |
| rank[i] = s[i]; |
| } |
|
|
| for (int k = 1; k < n; k <<= 1) { |
| auto cmp = [&](int i, int j) { |
| if (rank[i] != rank[j]) return rank[i] < rank[j]; |
| int ri = i + k < n ? rank[i + k] : -1; |
| int rj = j + k < n ? rank[j + k] : -1; |
| return ri < rj; |
| }; |
| sort(sa.begin(), sa.end(), cmp); |
| vector<int> tmp(n); |
| tmp[sa[0]] = 0; |
| for (int i = 1; i < n; i++) { |
| tmp[sa[i]] = tmp[sa[i - 1]] + cmp(sa[i - 1], sa[i]); |
| } |
| rank = tmp; |
| if (rank[sa[n - 1]] == n - 1) break; |
| } |
|
|
| int k = 0; |
| for (int i = 0; i < n; i++) { |
| if (rank[i] == 0) { |
| lcp[0] = 0; |
| continue; |
| } |
| int j = sa[rank[i] - 1]; |
| while (i + k < n && j + k < n && s[i + k] == s[j + k]) k++; |
| lcp[rank[i]] = k; |
| if (k > 0) k--; |
| } |
|
|
| lg.assign(n + 1, 0); |
| for (int i = 2; i <= n; i++) lg[i] = lg[i >> 1] + 1; |
|
|
| int K = lg[n] + 1; |
| st.assign(K, vector<int>(n)); |
| for (int i = 0; i < n; i++) st[0][i] = lcp[i]; |
|
|
| for (int j = 1; j < K; j++) { |
| for (int i = 0; i + (1 << j) <= n; i++) { |
| st[j][i] = min(st[j - 1][i], st[j - 1][i + (1 << (j - 1))]); |
| } |
| } |
| } |
|
|
| int get_lcp(int i, int j) { |
| if (i == j) return n - i; |
| int r1 = rank[i]; |
| int r2 = rank[j]; |
| if (r1 > r2) swap(r1, r2); |
| r1++; |
| int k = lg[r2 - r1 + 1]; |
| return min(st[k][r1], st[k][r2 - (1 << k) + 1]); |
| } |
| }; |
|
|
| bool check(int pos, int len, int n, int l, int k, const string& s, SuffixArray& sa) { |
| long long min_M_bad = 2e9; |
| int bad_cnt = 0; |
|
|
| for (int j = 0; j < k; j++) { |
| int p = j * l; |
| int L = min(len, sa.get_lcp(p, pos)); |
| long long M; |
| if (L < len) { |
| if (p + L < n && s[p + L] > s[pos + L]) { |
| M = max(l, L + 1); |
| } else { |
| M = 2e9; |
| } |
| } else { |
| M = max(l, len); |
| } |
|
|
| if (M == l) { |
| |
| } else { |
| bad_cnt++; |
| min_M_bad = min(min_M_bad, M); |
| } |
| } |
|
|
| if (bad_cnt < k) return true; |
| if (min_M_bad <= (long long)n - (long long)(k - 1) * l) return true; |
| return false; |
| } |
|
|
| void solve() { |
| int n, l, k; |
| if (!(cin >> n >> l >> k)) return; |
| string s; |
| cin >> s; |
|
|
| if ((long long)k * l > n) { |
| cout << "NO\n"; |
| return; |
| } |
|
|
| if (n == 1) { cout << "YES\n" << s << "\n"; return; } |
|
|
| SuffixArray sa; |
| sa.init(s); |
|
|
| vector<long long> cnt(n, 0); |
| vector<int> start_len(n, 0); |
|
|
| for (int r = 0; r < n; r++) { |
| int lcp_prev = (r == 0) ? 0 : sa.lcp[r]; |
| int st_len = max(l, lcp_prev + 1); |
| int en_len = n - sa.sa[r]; |
| if (st_len <= en_len) { |
| cnt[r] = en_len - st_len + 1; |
| start_len[r] = st_len; |
| } else { |
| cnt[r] = 0; |
| start_len[r] = 0; |
| } |
| } |
|
|
| vector<long long> pref(n, 0); |
| pref[0] = cnt[0]; |
| for (int r = 1; r < n; r++) { |
| pref[r] = pref[r - 1] + cnt[r]; |
| } |
|
|
| long long N_total = pref[n - 1]; |
| if (N_total == 0) { |
| cout << "NO\n"; |
| return; |
| } |
|
|
| auto get_substr = [&](long long idx) -> pair<int, int> { |
| int r = lower_bound(pref.begin(), pref.end(), idx) - pref.begin(); |
| long long prev = (r == 0) ? 0 : pref[r - 1]; |
| int len = start_len[r] + (idx - prev - 1); |
| return {sa.sa[r], len}; |
| }; |
|
|
| long long low = 1, high = N_total, ans_idx = 0; |
| while (low <= high) { |
| long long mid = low + (high - low) / 2; |
| auto [pos, len] = get_substr(mid); |
| if (check(pos, len, n, l, k, s, sa)) { |
| ans_idx = mid; |
| low = mid + 1; |
| } else { |
| high = mid - 1; |
| } |
| } |
|
|
| if (ans_idx == 0) { |
| cout << "NO\n"; |
| } else { |
| cout << "YES\n"; |
| auto [pos, len] = get_substr(ans_idx); |
| cout << s.substr(pos, len) << "\n"; |
| } |
| } |
|
|
| int main() { |
| ios_base::sync_with_stdio(false); |
| cin.tie(NULL); |
| int totalQueryNum; |
| if (cin >> totalQueryNum) { |
| while (totalQueryNum--) { |
| solve(); |
| } |
| } |
| return 0; |
| } |
