[LeetCode] #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.

本题是简单的全词匹配问题。时间8ms，代码如下：

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