Leetcode: Implement strStr()

Implement strStr().

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

Time Limit Exceeded

char *strStr(char *haystack, char *needle) {
        // Note: The Solution object is instantiated only once.
		if(!*needle)return haystack;
		while(*haystack != '\0')
		{
			if(*haystack == *needle)
			{
				char* h = haystack;
				char* n = needle;
				while(*h != '\0' && *n!= '\0' && *h==*n)h++,n++;
				if(*n=='\0')
					return haystack;
			}
			haystack++;
		}
		return NULL;
    }

优化:当haystack后面的长度小于needle的长度时就不用再匹配了。

Accepted

char *strStr(char *haystack, char *needle) {
        // Note: The Solution object is instantiated only once.
		if(!*needle)return haystack;
		char* pend = haystack;
		
		char* tmp = needle;
		while(*++tmp)pend++;

		while(*pend != '\0')
		{
			if(*haystack == *needle)
			{
				char* h = haystack;
				char* n = needle;
				while(*h != '\0' && *n!= '\0' && *h==*n)h++,n++;
				if(*n=='\0')
					return haystack;
			}
			haystack++;
			pend++;
		}
		return NULL;
    }