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.

思路：一种坏坏的解法

public class Solution {
    public int strStr(String haystack, String needle) {
        StringBuilder sb = new StringBuilder(haystack);
        int pos = sb.indexOf(needle);
        return pos;
    }
}

另一种：

public class Solution {
    public int strStr1(String haystack, String needle) {
    return haystack.indexOf(needle);
}

    public int strStr(String haystack, String needle) {
        if (haystack == null || needle == null) {
            return -1;
        }

        int l1 = haystack.length();
        int l2 = needle.length();

        for (int i = 0; i< l1-l2+1; i++){
            int count = 0;
            while (count < l2 && haystack.charAt (i+count) == needle.charAt(count))
                count++;
            if (count == l2) 
                return i; 
        }
        return -1;
    }
}