28. Find the Index of the First Occurrence in a String

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LeetCode

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Problem

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:

• $1 <= haystack.length, needle.length <= 10^4$
• haystack and needle consist of only lowercase English characters.

Code

class Solution {
    public int strStr(String haystack, String needle) {
        for(int i = 0; i <= haystack.length() - needle.length(); i++){
            if(haystack.charAt(i) == needle.charAt(0)){
                int j = 1;
                while(j < needle.length()){
                    if(haystack.charAt(i + j) != needle.charAt(j)) break;
                    j++;
                }

                if(j == needle.length()){
                    return i;
                }
            }
        }

        return -1;
    }
}