Implement strStr().

Returns a pointer to the first occurrence of needle in haystack, or null if

needle is not part of haystack.

public class Solution {

public String strStr(String haystack, String needle) {

// Start typing your Java solution below

// DO NOT write main() function

assert(haystack!=null && needle!=null);

if(needle.length()==0)

return haystack;

int i = 0;

while(i<haystack.length()) {

if(haystack.length()-i < needle.length())

break;

if(haystack.charAt(i)==needle.charAt(0)) {

int j = i;

while(j-i<needle.length() && haystack.charAt(j)==needle.charAt(j-i))

j++;

if(j-i==needle.length())

return haystack.substring(i);

}

i++;

}

return null;

}

}