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poj 2406(字尾陣列)

題意:給出一個串,是由它的一個子串重複k次得到的,問k最大是多少。
題解:從小到大列舉長度i,如果長度i的子串剛好是重複了len/i次,應該滿足len % i == 0和rank[0] - rank[i] == 1 和height[rank[0]] == len-i這些條件的,直接判斷就可以了,第一次用da倍增超時了(1000000的資料忘了。。。),換成dc3過了。

#include <cstdio>
#include <cstring>
#include <algorithm>
#define F(x) ((x) / 3 + ((x) % 3 == 1 ? 0 : tb))
#define G(x) ((x) < tb ? (x) * 3 + 1 : ((x) - tb) * 3 + 2) using namespace std; const int N = 1000005; int wa[N], wb[N], ws[N], wv[N], sa[N * 3]; int rank[N * 3], height[N * 3], s[N], n; char str[N]; int c0(int *r, int a, int b) { return r[a] == r[b] && r[a + 1] == r[b + 1] && r[a + 2
] == r[b + 2]; } int c12(int k, int *r, int a, int b) { if (k == 2) return r[a] < r[b] || r[a] == r[b] && c12(1, r, a + 1, b + 1); return r[a] < r[b] || r[a] == r[b] && wv[a + 1] < wv[b + 1]; } void sort(int *r, int *a, int *b, int n, int m) { for (int i = 0
; i < n; i++) wv[i] = r[a[i]]; for (int i = 0; i < m; i++) ws[i] = 0; for (int i = 0; i < n; i++) ws[wv[i]]++; for (int i = 1; i < m; i++) ws[i] += ws[i - 1]; for (int i = n - 1; i >= 0; i--) b[--ws[wv[i]]] = a[i]; } void dc3(int *r, int *sa, int n, int m) { int i, j, *rn = r + n, *san = sa + n, ta = 0, tb = (n + 1) / 3, tbc = 0, p; r[n] = r[n + 1] = 0; for (i = 0; i < n; i++) if (i % 3 != 0) wa[tbc++] = i; sort(r + 2, wa, wb, tbc, m); sort(r + 1, wb, wa, tbc, m); sort(r, wa, wb, tbc, m); for (p = 1, rn[F(wb[0])] = 0, i = 1; i < tbc; i++) rn[F(wb[i])] = c0(r, wb[i - 1], wb[i]) ? p - 1 : p++; if (p < tbc) dc3(rn, san, tbc, p); else for (i = 0; i < tbc; i++) san[rn[i]] = i; for (i = 0; i < tbc; i++) if (san[i] < tb) wb[ta++] = san[i] * 3; if (n % 3 == 1) wb[ta++] = n - 1; sort(r, wb, wa, ta, m); for (i = 0; i < tbc; i++) wv[wb[i] = G(san[i])] = i; for (i = 0, j = 0, p = 0; i < ta && j < tbc; p++) sa[p] = c12(wb[j] % 3, r, wa[i], wb[j]) ? wa[i++] : wb[j++]; for (; i < ta; p++) sa[p] = wa[i++]; for (; j < tbc; p++) sa[p] = wb[j++]; } void calheight(int *r, int *sa, int n) { int i, j, k = 0; for (i = 1; i <= n; i++) rank[sa[i]] = i; for (i = 0; i < n; height[rank[i++]] = k) for (k ? k-- : 0, j = sa[rank[i] - 1]; r[i + k] == r[j + k]; k++); } int main() { while (scanf("%s", str) == 1 && str[0] != '.') { int len = strlen(str); for (int i = 0; i < len; i++) s[i] = str[i] - 'a' + 1; s[len] = 0; dc3(s, sa, len + 1, 105); calheight(s, sa, len); int flag = 0; for (int i = 1; i <= len; i++) { if (len % i == 0 && rank[0] == rank[i] + 1 && height[rank[0]] == len - i) { printf("%d\n", len / i); flag = 1; break; } } if (!flag) printf("1\n"); } return 0; }