UVA 1328 - Period (KMP)

Posted 2020-09-19 jzssuanfa

UVA 1328 - Period

题目链接

题意：给定一个字符串，求出有几个位置的前缀串是由个数大于1的串循环得到的。求出位置和循环次数

思路：利用kmp的next数组的性质，i - next[i]就是循环长度，然后推断一下是不是正好是倍数就可以

代码：

#include <cstdio>
#include <cstring>

const int N = 1000005;

int n, next[N];
char str[N];

int main() {
    int cas = 0;
    while (~scanf("%d", &n) && n) {
	scanf("%s", str + 1);
	next[1] = 0;
	int j = 0;
	for (int i = 2; i <= n; i++) {
	    while (j && str[i] != str[j + 1]) j = next[j];
	    if (str[i] == str[j + 1]) j++;
	    next[i] = j;
	}
	printf("Test case #%d\n", ++cas);
	for (int i = 1; i <= n; i++) {
	    if (!next[i]) continue;
	    if (i % (i - next[i])) continue;
	    printf("%d %d\n", i, i / (i - next[i]));
	}
	printf("\n");
    }
    return 0;
}