UVA3026Period(最短循环节)
题意: 给定长度为n的字符串s,求他的每个前缀的最短循环节
分析: kmp预处理 next[]数组,然后对于 前 i 个字符,如果 next[i] > 0 && i % (i - next[i] ),前 i 个字符的循环节就是(i -1, ... i - next[i])
从 0 到 n - next[n] 是最小覆盖串,从 n - next[n] ... n-1就是循环节
#include <iostream> #include <cstdio> #include <algorithm> #include <cstring> using namespace std; const int Max = 1e6 + 10; char str[Max]; int Next[Max]; void pre_kmp(int n) { int i = 0, k = -1; Next[0] = -1; while (i < n) { while (k != -1 && str[k] != str[i]) k = Next[k]; Next[++i] = ++k; } } int main() { int test = 0; int n; while (scanf("%d", &n) != EOF && n) { getchar(); scanf("%s", str); pre_kmp(n); printf("Test case #%d\n", ++test); for (int i = 2; i <= n; i++) { if (Next[i] > 0 && i % (i - Next[i]) == 0) printf("%d %d\n", i, i / (i - Next[i])); } printf("\n"); } }