28. Find the Index of the First Occurrence in a String(Solution || Leetcode medium || Java)

Runtime: 0 ms, faster than 100.00% of Java online submissions for Find the Index of the First Occurrence in a String.

Memory Usage: 40.4 MB, less than 84.90% of Java online submissions for Find the Index of the First Occurrence in a String.

Given two strings needle and haystack, return the index of the first occurrence of needle in haystack, or -1 if needle is not part of haystack.

Example 1:

Input: haystack = "sadbutsad", needle = "sad"
Output: 0
Explanation: "sad" occurs at index 0 and 6.
The first occurrence is at index 0, so we return 0.

Example 2:

Input: haystack = "leetcode", needle = "leeto"
Output: -1
Explanation: "leeto" did not occur in "leetcode", so we return -1.

Constraints:

• 1 <= haystack.length, needle.length <= 104
• haystack and needle consist of only lowercase English characters.

SOLUTION:

class Solution {
    public int strStr(String haystack, String needle) {
       int h =  haystack.length();
       int n = needle.length();
        
         if(h < n){
             return -1;
         }
  
    //We will use two pointers that will search for needle as a substring
        int j = 0;
        
        for(int i = n - 1; i < h; i++){
            if( haystack.substring(j,i+1).equals(needle)){
                return j;
            }
            else{
                j++;
            }
        }
       
        return -1;
    }
}

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