28. Implement strStr()

Implement strStr().

Returns the index of the first occurrence of needle in haystack, or -1 if needle is not part of haystack.

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Seen this question in a real interview before?   

Yes

 

给定字符串A和字符串B，查看B是否是A的子串，如果是，返回B在A串中的首字母的指针索引，如果没有，则返回-1

class Solution {
public:
    int strStr(string haystack, string needle) {
        for(int i=0;;i++)
		{
			for(int j=0;;j++)
			{
				if(j==needle.size())
					return i;
				if(i+j == haystack.size())
					return -1;
				if(needle[j]!=haystack[i+j])
					break;
			}
		}
    }
};

或者感觉前面的难懂：可以这样：

class Solution {
public:
    int strStr(string haystack, string needle) {
        if(needle.empty())
			return 0;
		int h1 = haystack.length();
		int h2 = needle.length();
		if(h1<h2)
			return -1;
		if(h1==h2)
			return haystack==needle ? 0 : -1;
		int i;
		for(i=0;i<h1;i++)
		{
			bool found=true;
			for(int j=0;j<h2;j++)
			{
				if(haystack[i+j]!=needle[j])
				{
					found = false;
					break;
				}
			}
			if(found)    //如果在i=0的时候完美匹配，那么就直接跳出循环
				break;
		}
		return i > h1-h2 ? -1 : i;
    }
};