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: 2
Example 2:
Input: haystack = “aaaaa”, needle = “bba”
Output: -1
Clarification: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;
}
}