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.

Question link: https://leetcode.com/problems/implement-strstr/
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class Solution {
    public int strStr(String haystack, String needle) {
    
        if(needle.length() == 0){
            return 0;
        }
        
        String s = "";
        char c;
        int endIndex = 0;
        for(int i = 0; i<haystack.length(); i++){
            
            if(needle.length() == 1){
                c = haystack.charAt(i);
                if(c == needle.charAt(0)){
                    return i;
                }
            }
            else {
                
                endIndex = i + needle.length();
                if(endIndex > haystack.length()){
                    break;
                }
                else{
                    s = haystack.substring(i,endIndex);
                    System.out.print(s + " ");
                }

                if(s.equals(needle)){
                    return i;
                }   
        }        
    }
        return -1;
    }
}