Leetcode: Implement strStr()

最新推荐文章于 2019-09-08 17:47:58 发布

原创最新推荐文章于 2019-09-08 17:47:58 发布 · 2.5k 阅读

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#Leetcode #strStr

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本文介绍了一个字符串查找函数strStr()的两种实现方式：一种是直接逐字符对比，另一种是在确定haystack剩余长度小于needle长度时提前终止搜索以提高效率。

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;
    }