LeetCode Implement strStr()

Implement strStr()

Implement strStr().

Returns a pointer to the first occurrence of needle in haystack, or null if needle is not part of haystack.

写了好几种求next数组的方法，都可以通过。

class Solution {
public:
    char *strStr(char *haystack, char *needle) {
        int l_need = strlen(needle);
        if(l_need == 0) return haystack;
        int l_hay = strlen(haystack);
        if(l_hay == 0)    return NULL;

        int idx = match(haystack, needle, l_hay, l_need);
        if(idx >= 0)
            return haystack+idx;
       
        return NULL;
    }

    int match(char* s, char* p, int ls, int lp)
    {
        vector<int> next(lp);
        int i = 0;
        int j = 0;
        getnext3(p, lp, next);
        while(i < strlen(s))
    	{
			if(-1 == j || s[i] == p[j])
			{
				++i;
				++j;
			}
			else
				j = next[j];
			if(j == lp)
				return i - lp;
		}
        return -1;
    }

    void getnext1(const char* p, int lp, vector<int>& next)
    {
        next[0] = -1;
		int i = 0;
		while(i < lp - 1)
		{
			int idx = i >= 0? next[i]: -1;
			if(-1 == idx)
				next[++i] = ++idx;
			else if(p[i] == p[idx])
				next[++i] = ++idx;
			else
			{
				while(idx >= 0 && p[i] != p[idx])
					idx = next[idx];
				next[++i] = ++idx;
			}
		}
    }
	void getnext2(const char* p, int lp, vector<int>& next)
    {
        int j = 0, k = -1;
        next[0] = -1;
        while(j < lp - 1)
        {
            if(k == -1 || p[j] == p[k])
            {
                ++j;
                ++k;
                next[j] = k;
            }
            else
                k = next[k];
        }
    }

	void getnext3(const char*p, int lp, vector<int>& next)
	{
		next[0] = -1;
		for(int i = 1; i < lp; ++i)
		{
			int idx = next[i-1];
			if(-1 == idx)
				next[i] = 0;
			else if(p[i-1] == p[idx])
				next[i] = ++idx;
			else
			{
				while(idx >= 0 && p[i-1] != p[idx])
					idx = next[idx];
				next[i] = ++idx;
			}
		}
	}
};