Implement strStr().
Return the index of the first occurrence of needle in haystack, or -1 if needle is not part of haystack.
Example：
Input: haystack = "hello", needle = "ll"
Output: 2
Input: haystack = "aaaaa", needle = "bba"
Output: -1
Clarification：
What should we return when
needleis an empty string? This is a great question to ask during an interview.
For the purpose of this problem, we will return 0 whenneedleis an empty string. This is consistent to C's strstr() and Java's indexOf().
解释下题目：
实现java的indexOf()方法
1. 挨个判断
实际耗时：6ms
public int strStr(String haystack, String needle) {
if (needle.equals("") || null == needle) {
return 0;
}
//最多循环haystack.length() - needle.length()次
for (int i = 0; i <= haystack.length() - needle.length(); i++) {
int now = i; //记录目前的haystack中的索引
int count = 0; //匹配上的个数
for (int j = 0; j < needle.length(); j++) {
if (haystack.charAt(now) != needle.charAt(j)) {
break;
} else {
count++;
now++;
}
if (count == needle.length()) {
return i;
}
}
}
return -1;
}
思路：那除了挨个判断还能怎么做呢？
