Needle in HayStack

Problem Statement

Implement strStr().

Returns the index of the first occurrence of needle in haystack, or -1 if needle is not part of haystack.

Link to GitHub Java : Code
Link to GitHub JavaScript Code




Understanding the problem statement

This question is confusing. lets understand the problem

The fundamental string searching (matching) problem is defined as follows: given two strings – a text and a pattern, determine whether the pattern appears in the text. The problem is also known as “the needle in a haystack problem.”

Example:

Example 1
s="strstr"
needle="Str"
output=-1

Example 2
s="strStr"
needle="Str"
output=3

Example 3
s="strstr"
needle="str"
output=0

Solution

• We need 2 loops with i and j counters
• We need compare the characters from actual string with that to the needle.
• We would only increment j counter if we find the character in the string matches character in the needle
• If needle length matches j counters we need to return i else return -1 

public static int get(String haystack, String needle)
 {
  for(int i=0;;i++){
   for(int j=0;;j++){
    if(j==needle.length()) return i;
    if(i+j==haystack.length()) return -1;
    if(needle.charAt(j)!=haystack.charAt(i+j))
     {break;}
         }
  }
 }

Iteration