class Solution:
    def longestCommonPrefix(self, arr1, arr2):
        arr1_prefixes = set() 
        
        # Step 1: Build all possible prefixes from arr1
        for val in arr1:
            while val not in arr1_prefixes and val > 0:
                arr1_prefixes.add(val)
                val //= 10
                
        longest_prefix = 0
        
        # Step 2: Check each number in arr2
        for val in arr2:
            while val not in arr1_prefixes and val > 0:
                val //= 10
            if val > 0:
                longest_prefix = max(longest_prefix, len(str(val)))
                
        return longest_prefix