LeetCode 28: Implement strStr()

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

public class Solution {
    public int strStr(String haystack, String needle) {
        // Brute-force substring search
        int n = haystack.length();
        int m = needle.length();
        
        for (int i = 0; i <= n-m; i++)
        {
            int j;
            
            for (j = 0; j < m; j++)
                if (haystack.charAt(i+j) != needle.charAt(j))
                    break;
            
            // Found        
            if (j == m)
                return i;
        }
        
        // Not found
        return -1;
    }
}