UVA 12012 - Detection of Extraterrestrial(KMP)

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UVA 12012 - Detection of Extraterrestrial

题目链接

题意：给定一个字符串，求其所有子串中，对应1-n循环次数的最长串长度

思路：KMP，n才1000，可以接受O(n^2)的算法，对于每个后缀串，做一次KMP，然后在遍历一遍KMP数组，这样就可以得到每个子串的所有循环次数了，然后不断更新答案即可

代码：

#include <cstdio>#include <cstring>#include <algorithm>using namespace std;const int N = 1005;int t, ans[N], n, l, r, m, next[N];char str[N], s[N];void getnext() {    next[0] = next[1] = 0;    int j = 0;    for (int i = 2; i <= m; i++) {while (j && s[i - 1] != s[j]) j = next[j];if (s[i - 1] == s[j]) j++;next[i] = j;    }}int main() {    int cas = 0;    scanf("%d", &t);    while (t--) {memset(ans, 0, sizeof(ans));scanf("%s", str);n = strlen(str);for (int i = 0; i < n; i++) {    m = 0;    for (int j = i; j < n; j++)s[m++] = str[j];    getnext();    for (int j = 1; j <= m; j++) {int tmp = j;while (tmp) {    if (j % (j - next[tmp]) == 0) {int ti = j / (j - next[tmp]);ans[ti] = max(ans[ti], j);    }    tmp = next[tmp];}    }}printf("Case #%d:", ++cas);for (int i = 1; i <= n; i++)    printf(" %d", ans[i]);printf("\n");    }    return 0;}

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