Leetcode: Longest Common Prefix

Write a function to find the longest common prefix string amongst an array of strings.

public class Solution {
    public String longestCommonPrefix(String[] strs) {
        if (strs == null) {
            return null;
        }
        
        if (strs.length == 0) {
            return "";
        }
        
        String res = strs[0];
        for (int i = 1; i < strs.length; i++) {
            String curr = strs[i];
            StringBuilder sb = new StringBuilder();
            int j = 0;
            while (j < res.length() && j < curr.length() && res.charAt(j) == curr.charAt(j)) {
                sb.append(res.charAt(j));
                j++;
            }
            res = sb.toString();
        }
        return res;
    }
}