Implement 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: 2Example 2:Input: haystack = “aaaaa”, needle = “bba"Output: -1Clarification:What should we return when needle is an empty string? This is a great question to ask during an interview.For the purpose of this problem, we will return 0 when needle is an empty string. This is consistent to C’s strstr() and Java’s indexOf().难度: easy题目：实现方法strstr() 返回首次needle出现在haystack中的索引，如果不存在则返回 -1.Runtime: 7 ms, faster than 37.21% of Java online submissions for Implement strStr().Memory Usage: 26.9 MB, less than 32.93% of Java online submissions for Implement strStr().class Solution { public int strStr(String haystack, String needle) { if (needle.length() > haystack.length()) { return -1; } for (int i = 0; i <= haystack.length() - needle.length(); i++) { int j = 0; for (; j < needle.length(); j++) { if (haystack.charAt(i + j) != needle.charAt(j)) { break; } } if (j == needle.length()) { return i; } } return -1; }}