114 lines
3.0 KiB
C++
114 lines
3.0 KiB
C++
#include <cstdio>
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#include <cstring>
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#include <vector>
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#include <algorithm>
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using namespace std;
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const int maxn = 1e5+5;
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typedef long long ll;
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struct Suffix_Arr {
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char s[maxn];
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int n, SA[maxn], rank[maxn], height[maxn];
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int tmp_one[maxn], tmp_two[maxn], c[maxn];
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ll f[maxn];
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void init ();
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void build(int m);
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void get_height();
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void solve ();
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bool judge(ll m);
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}AC;
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int K;
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int main () {
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while (scanf("%d", &K) == 1 && K) {
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AC.init();
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AC.build(256);
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AC.get_height();
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AC.solve();
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}
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return 0;
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}
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bool Suffix_Arr::judge(ll m) {
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int t = lower_bound(f + 1, f + n + 1, m) - f;
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int R = n - (f[t] - m + 1);
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int len = R - SA[t] + 1;
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memset(c, -1, sizeof(c));
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c[SA[t]] = len;
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for (int i = t+1; i <= n; i++) {
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len = min(len, height[i]);
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if (len == 0)
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return false;
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c[SA[i]] = len;
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}
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int ret = 0, p = n + 1;
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for (int i = 0; i < n; i++) {
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if (i == p) {
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ret++;
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p = n + 1;
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}
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if (c[i] != -1)
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p = min(p, i + c[i]);
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if (ret >= K)
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return false;
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}
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return true;
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}
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void Suffix_Arr::solve() {
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ll l = 1, r = f[n];
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for (int i = 0; i < 70; i++) {
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ll mid = (l + r) / 2;
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if (judge(mid))
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r = mid;
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else
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l = mid;
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}
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int t = lower_bound(f + 1, f + n + 1, r) - f;
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int len = n - (f[t] - r + 1);
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for (int i = SA[t]; i <= len; i++)
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printf("%c", s[i]);
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printf("\n");
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}
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void Suffix_Arr::init() {
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scanf("%s", s);
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n = strlen(s) + 1;
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}
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void Suffix_Arr::get_height() {
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for (int i = 0; i < n; i++)
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rank[SA[i]] = i;
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int mv = height[n-1] = 0;
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for (int i = 0; i < n - 1; i++) {
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if (mv) mv--;
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int j = SA[rank[i] - 1];
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while (s[i+mv] == s[j+mv])
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mv++;
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height[rank[i]] = mv;
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}
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n--;
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f[0] = 0;
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for (int i = 1; i <= n; i++)
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f[i] = f[i-1] + n - SA[i] - height[i];
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}
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void Suffix_Arr::build(int m) {
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int *x = tmp_one, *y = tmp_two;
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for (int i = 0; i < m; i++) c[i] = 0;
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for (int i = 0; i < n; i++) c[x[i] = s[i]]++;
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for (int i = 1; i < m; i++) c[i] += c[i-1];
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for (int i = n - 1; i >= 0; i--) SA[--c[x[i]]] = i;
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for (int k = 1; k <= n; k <<= 1) {
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int mv = 0;
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for (int i = n - k; i < n; i++) y[mv++] = i;
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for (int i = 0; i < n; i++) if (SA[i] >= k)
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y[mv++] = SA[i] - k;
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for (int i = 0; i < m; i++) c[i] = 0;
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for (int i = 0; i < n; i++) c[x[y[i]]]++;
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for (int i = 1; i < m; i++) c[i] += c[i-1];
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for (int i = n - 1; i >= 0; i--) SA[--c[x[y[i]]]] = y[i];
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swap(x, y);
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mv = 1;
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x[SA[0]] = 0;
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for (int i = 1; i < n; i++)
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x[SA[i]] = (y[SA[i-1]] == y[SA[i]] && y[SA[i-1] + k] == y[SA[i] + k] ? mv - 1 : mv++);
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if (mv >= n)
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break;
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m = mv;
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}
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}
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