题目描述：
Implement strStr().
Returns the index of the first occurrence of needle in haystack, or -1 if needle is not part of haystack.
Update (2014-11-02):
The signature of the function had been updated to return the index instead of the pointer. If you still see your function signature returns a char * or String, please click the reload button to reset your code definition.
解题思路：
从开头开始，逐个匹配。
注意特殊情况。
代码如下：
public class Solution {
public static int strStr(String haystack, String needle) {
int haystackLength = haystack.length();
int needleLength = needle.length();
int j = 1;
if (needleLength == 0)
return 0;
if (needleLength > haystackLength)
return -1;
for (int i = 0; i <= haystackLength - needleLength; i++) {
if (haystack.charAt(i) == needle.charAt(0)) {
for (j = 1; j < needleLength; j++) {
if (haystack.charAt(i + j) != needle.charAt(j))
break;
}
if (j == needleLength)
return i;
}
}
return -1;
}
}