# [LeetCode 28] Implement strStr

### Question

Implement strStr().

Returns a pointer to the first occurrence of needle in haystack, or null if needle is not part of haystack.

### Stats

 Frequency 5 Diffficulty 4 Adjusted Difficulty 4 Time to use ----------

Ratings/Color = 1(white) 2(lime) 3(yellow) 4/5(red)

### Analysis

There are 2 ways to solve this problem.

1. Most common way is using 2 nested loop

2. Also can be solved by KPM algorithm

### Solution

Standard solution is posted below. Read this post for more.

As for KMP algo, I have to admit I am not able to do it. Plz refer to this blog and this blog for more!

### My code

``````public class Solution {
public int strStr(String haystack, String needle) {
if (haystack == null || needle == null) {
return -1;
} else if (haystack.length() < needle.length()) {
return -1;
} else if (haystack.length() == 0 && needle.length() == 0) {
return 0;
}
for (int i = 0; i <= haystack.length() - needle.length(); i++) {
int j;
// try to match part of haystack (starting from i) to needle
for (j = 0; j < needle.length(); j++) {
if (haystack.charAt(i + j) != needle.charAt(j)) {
break;
}
}
// if part of haystack (starting from i) matches needle
if (j == needle.length()) {
return i;
}
// if not match, proceed to next loop
}
return -1;
}
}
``````