import java.util.ArrayList;

import java.util.List;

public class FindCommonCharacters {

public List<String> commonChars(String[] A) {

List<String> res = new ArrayList<>();

int n = A.length;

int[][] alphabet = new int[n][26];

for(int i = 0; i < n; i++){

for(char ch : A[i].toCharArray()){

alphabet[i][ch - 'a']++;

}

}

for(int i = 0; i < 26; i++){

int min = alphabet[0][i];

for(int j = 1; j < n; j++){

if(min > alphabet[j][i]) min = alphabet[j][i];

}

for(int k = 0; k < min; k++) res.add(String.valueOf((char)(i + 'a')));

}

return res;

}

public static void main(String[] args) {

FindCommonCharacters findCommonCharacters = new FindCommonCharacters();

System.out.println(findCommonCharacters.commonChars(new String[]{"bella","label","roller"}));

System.out.println(findCommonCharacters.commonChars(new String[]{"cool","lock","cook"}));

System.out.println(findCommonCharacters.commonChars(new String[]{"cool","lock",""}));

System.out.println(findCommonCharacters.commonChars(new String[]{"aaaa","aaa","aaaaaaa"}));

System.out.println(findCommonCharacters.commonChars(new String[]{"aaaa"}));

}

}