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.

分析：

给出两个字符串，查询第二个字符串是否在第一个字符串中出现过，如果有，就返回第一次出现的位置。

If source = "source" and target = "target", return -1.

If source = "abcdabcdefg" and target = "bcd", return 1.

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