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| #include<iostream> #include<stdio.h> #include<cstring> #include<string> #include<vector> #include<algorithm> using namespace std; const int maxn = 1e5 + 5; int t, n, q; int cnt, root[maxn]; int rk[maxn], tmp[maxn], k, sa[maxn]; int lcp[maxn], st[maxn][21]; char s[maxn]; int read() { int x = 0, f = 1; char s = getchar(); for (; s > '9' || s < '0'; s = getchar()) if (s == '-') f = -1; for (; s >= '0'&&s <= '9'; s = getchar()) x = x * 10 + s - '0'; return x * f; } void clear() { cnt = 0; k = 0; memset(root, 0, sizeof(root)); memset(rk, 0, sizeof(rk)); memset(tmp, 0, sizeof(tmp)); memset(sa, 0, sizeof(sa)); memset(lcp, 0, sizeof(lcp)); memset(st, 0x3f, sizeof(st)); }
struct node { int l, r, sum; }T[maxn*40]; void update(int l, int r, int &x, int y, int pos) { T[++cnt] = T[y]; T[cnt].sum++; x = cnt; if (l == r)return; int mid = (l + r) >> 1; if (mid >= pos)update(l, mid, T[x].l, T[y].l, pos); else update(mid + 1, r, T[x].r, T[y].r, pos); } int query(int l, int r, int x, int y, int k) { if (l == r)return l; int mid = (l + r) >> 1; int sum = T[T[y].l].sum - T[T[x].l].sum; if (sum >= k)return query(l, mid, T[x].l, T[y].l, k); else return query(mid + 1, r, T[x].r, T[y].r, k - sum); }
bool compare_sa(int i, int j) { if (rk[i] != rk[j])return rk[i] < rk[j]; else { int ri = i + k <= n ? rk[i + k] : -1; int rj = j + k <= n ? rk[j + k] : -1; return ri < rj; } } void constract_sa(const char* S) { for (int i = 0; i <= n; i++) { sa[i] = i; rk[i] = i < n ? S[i] : -1; } for (k = 1; k <= n; k *= 2) { sort(sa, sa + n + 1, compare_sa); tmp[sa[0]] = 0; for (int i = 1; i <= n; i++) { tmp[sa[i]] = tmp[sa[i - 1]] + (compare_sa(sa[i - 1], sa[i]) ? 1 : 0); } for (int i = 0; i <= n; i++) { rk[i] = tmp[i]; } } } void constract_lcp(const char* S) { for (int i = 0; i <= n; i++) { rk[sa[i]] = i; } int h = 0; lcp[1] = 0; for (int i = 0; i < n; i++) { int j = sa[rk[i] - 1]; if (h > 0)h--; for (; j + h < n&&i + h < n; h++) { if (S[j + h] != S[i + h])break; } lcp[rk[i]] = h; } for(int i=1;i<=n;i++) st[i][0] = lcp[i]; for (int j = 1; j <= 20; j++) for (int i = 1; i + (1 << j) - 1 <= n; ++i) st[i][j] = min(st[i][j - 1], st[i + (1 << (j - 1))][j - 1]); } int LCP(int i, int j) { if (i - 1 == j)return n - sa[i - 1]; int x = log2(j - i + 1); return min(st[i][x], st[j - (1 << x) + 1][x]); }
void solve(int S, int T, int k) { int L, R, l, r; l = 1; r = rk[S]; while (l <= r) { int mid = (l + r) / 2; if (LCP(mid+1, rk[S]) >= (T - S + 1)) { L = mid; r = mid - 1; } else { l = mid + 1; } } l = rk[S]; r = n; while (l <= r) { int mid = (l + r) / 2; if (LCP(rk[S]+1, mid) >= (T - S + 1)) { R = mid; l = mid + 1; } else { r = mid - 1; } } if (R - L + 1 < k) { cout << "-1" << endl; return; } cout << query(1, n, root[L - 1], root[R], k) << endl; } int main() { t = read(); while (t--) { clear(); n = read(); q = read(); scanf("%s", s); constract_sa(s); constract_lcp(s); for (int i = 1; i <= n; i++) { update(1, n, root[i], root[i - 1], sa[i]+1); } while (q--) { int l, r, K; l = read(); r = read(); K = read(); l--; r--; solve(l, r, K); } } return 0; }
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