28. Find the index of the first occurrence in a string

Easy

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) {
        boolean exist = false;
        if(haystack.contains(needle)){
            exist = true;
        }
        
        int n = -1;
        
        if(exist){
            for(int i=0;i<haystack.length()-needle.length()+1;i++){
                if(haystack.substring(i,i+needle.length()).equals(needle)){
                    n = i;
                    break;
                }
            }
        }
        return n;
        
    }
}