力扣459. 重复的子字符串（字符串相加，去除首尾字符版）

class Solution {
public:
    vector<int> getNext(string s) {
        vector<int> next(s.size(), 0);
        int j = 0;
        for(int i = 1; i < s.size(); i++) {
            while(j > 0 && s[i] != s[j]) {
                j = next[j - 1];
            }
            if(s[i] == s[j]) {
                j++;
            }
            next[i] = j;
        }
        return next;
    }

    bool repeatedSubstringPattern(string s) {
        string doubleS = s + s;
        doubleS.erase(0, 1);
        doubleS.erase(doubleS.size() - 1);
        int m = s.size();
        int n = doubleS.size();

        vector<int> next = getNext(s);
        int i = 0, j = 0;
        while(i < n) {
            while(j > 0 && doubleS[i] != s[j]) {
                j = next[j - 1];
            }
            if(doubleS[i] == s[j]) {
                j++;
            }
            i++;
            if(j == m) {
                return true;
            }
        }
        return false;
    }
};