28. Implement strStr()【easy】

28. Implement strStr()【easy】

Implement strStr().

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

解法一：

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