28.实现-str-str.cpp

/*
 * @lc app=leetcode.cn id=28 lang=cpp
 *
 * [28] 实现 strStr()
 */

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