1002. Find Common Characters

Given an array A of strings made only from lowercase letters, return a list of all characters that show up in all strings within the list (including duplicates).  For example, if a character occurs 3 times in all strings but not 4 times, you need to include that character three times in the final answer.

You may return the answer in any order.

Example 1:

Input: ["bella","label","roller"]
Output: ["e","l","l"]

Example 2:

Input: ["cool","lock","cook"]
Output: ["c","o"]

Note:

1. 1 <= A.length <= 100
2. 1 <= A[i].length <= 100
3. A[i][j] is a lowercase letter

use hash table

time: O(n), space = O(n)

class Solution {
    public List<String> commonChars(String[] A) {
        int[] countMin = new int[26];
        Arrays.fill(countMin, Integer.MAX_VALUE);
        
        for(String s : A) {
            int[] cnt = new int[26];
            for(int i = 0; i < s.length(); i++) {
                cnt[s.charAt(i) - 'a']++;
            }
            for(int i = 0; i < 26; i++) {
                countMin[i] = Math.min(cnt[i], countMin[i]);
            }
        }
        
        List<String> res = new ArrayList<>();
        for(char c = 'a'; c <= 'z'; c++) {
            while(countMin[c - 'a'] > 0) {
                res.add(String.valueOf(c));
                countMin[c - 'a']--;
            }
        }
        
        return res;
    }
}