LeetCode 459

计算next数组，由本题可以引出两个结论：

1. t = n - next[n] 是这个字符串最小循环节的长度
2. 最后一节可能不满n - next[n]

class Solution {
    public boolean repeatedSubstringPattern(String s) {
        int n = s.length();
        s = " " + s;
        char[] cs = s.toCharArray();
        int[] next = new int[n + 1];
        for (int i = 2, j = 0; i <= n; i++) {
            while (j > 0 && cs[i] != cs[j + 1]) j = next[j];
            if (cs[i] == cs[j + 1]) j++;
            next[i] = j;
        }
        int t = n - next[n];
        return t < n && n % t == 0;
    }
}