28. Implement strStr()

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().

  • TODO: implement KMP

  • Brutal Force

    public int strStr(String s, String w) {
  if(w.length()==0) return 0;
  for(int i = 0; i < s.length() - w.length()+1 ; i++) {
      for(int j = 0; j < w.length(); j++) {
          if(s.charAt(i+j) != w.charAt(j))
              break;
          if(j == w.length()-1)
              return i;
      }
  }
  return -1;
}