Implement strStr()

Implement strStr().

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

字符串匹配问题，要注意needle 为空的情况，最简单的代码是:

public class Solution {
    public int strStr(String haystack, String needle) {
        return haystack.indexOf(needle);
    }
}

当然这样写就没啥意义了。

完整代码:

public class Solution {
    public int strStr(String haystack, String needle) {
        int size1 = haystack.length();
        int size2 = needle.length();
        if(size2==0) return 0;
        int gap = size1-size2;
        for(int i=0;i<=gap;i++) {
            for(int j=0;j<size2;j++) {
                if(haystack.charAt(j+i)!=needle.charAt(j)) break;
                else if(j==size2-1) return i;
            }
        }
        return -1;
    }
}