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.

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().

Example 1:

Input: haystack = "hello", needle = "ll"
Output: 2

Example 2:

Input: haystack = "aaaaa", needle = "bba"
Output: -1

Example 3:

Input: haystack = "", needle = ""
Output: 0

Constraints:

• 0 <= haystack.length, needle.length <= 5 * 104

• haystack and needle consist of only lower-case English characters.

public class Solution {
    public int StrStr(string haystack, string needle) {
      if(haystack != null && needle == ""){
        return 0;
      }

      // if(haystack == needle){
      //   return 0;
      // }
      
      var h_l = haystack.Length;
      var n_l = needle.Length;
      
      for(int i = 0; i <= (h_l - n_l); i++){
          var j = 0;
          while(j < n_l && haystack[i+j] == needle[j]){
            j++;
          }
          if(j == n_l){
            return i;
          }
        }
      
        return -1;
      }
      
    }