leetcode -- Implement strStr()

Implement strStr().

Returns a pointer to the first occurrence of needle in haystack, or null if needle is not part of haystack.

此题应用KMP算法来解，但忘记了，写了个普通解

line 10: 当needle == "" 时， 返回haystack

line 11: 循环终止条件需注意

public class Solution {
    public static String strStr(String haystack, String needle) {
        // Start typing your Java solution below
        // DO NOT write main() function
        int needleLen = needle.length();
        int haystackLen = haystack.length();
        if (needleLen > haystackLen)
            return null;

        if (needleLen == 0)
            return haystack;
            
        int i = 0;
        for (; i < haystackLen - needleLen + 1;) {
            int j = 0;
            for (; j < needleLen;) {
                if (needle.charAt(j) == haystack.charAt(i)) {
                    i++;
                    j++;
                } else {
                    break;
                }
            }
            if (j == needleLen) {
                i = i - j;
                return haystack.substring(i, haystackLen);
            } else {
                i = i - j + 1;
            }

        }

        return null;
    }
}