LeetCode Ex28 Implement strStr()

Implement strStr()

mplement strStr().
Return the index of the first occurrence of needle in haystack, or -1 if needle is not part of haystack.
Example 1:
Input: haystack = "hello", needle = "ll"
Output: 2
Example 2:
Input: haystack = "aaaaa", needle = "bba"
Output: -1
题目

该题要求返回needle在haystack中第一次出现的位置，即String类的indexOf方法。

    public int strStr(String haystack, String needle) {
        int l1 = haystack.length(), l2 = needle.length();
        if (l1 < l2) {
            return -1;
        } else if (l2 == 0) {
            return 0;
        }
        int threshold = l1 - l2;
        for (int i = 0; i <= threshold; ++i) {
            if (haystack.substring(i, i + l2).equals(needle)) {
                return i;
            }
        }
        return -1;
    }