【LeetCode】28. 找出字符串中第一个匹配项的下标 -- 459. 重复的子字符串

28. 找出字符串中第一个匹配项的下标

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

459. 重复的子字符串

class Solution {
public:
    bool repeatedSubstringPattern(string s) {
        return (s + s).find(s, 1) != s.size();
    }
};