1002. Find Common Characters

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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 <= A.length <= 100
1 <= A[i].length <= 100
A[i][j] is a lowercase letter
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//首先数列中的每个字符串需要对26个字母统计频率，
//然后要比较所有字符串里面每个字母的频率，取最小值，就是在所有字符串里面出现的频率，并且是包括重复的情况。
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// TC: O(m * n) 
// SC: O(1) 

class Solution {
    public List<String> commonChars(String[] A) {
        int len = A.length;
        int[][] count = new int[len][26];
        
        for (int i = 0; i < len; i ++) {
            for (char c : A[i].toCharArray()) {
                count[i][c - 'a'] ++;
            }
        }
        
        List<String> result = new ArrayList();
        String s; 
        for (int i = 0; i < 26; i ++) {
            int min = 100;
            
            for (int j = 0; j < len; j ++) {
                min = Math.min(min, count[j][i]);
            }
            
            for (int k = 0; k < min; k ++) {
                s = String.valueOf((char)(i + 'a'));
                result.add(s);
            }
        }
        
        return result;
    }
}