1002.CommonChars.cs

// 1002. Find Common Characters
// Given a string array words, return an array of all characters that show up in all strings within the words (including duplicates). You may return the answer in any order.

// Example 1:
// Input: words = ["bella","label","roller"]
// Output: ["e","l","l"]
// Example 2:
// Input: words = ["cool","lock","cook"]
// Output: ["c","o"]

// Constraints:
// 1 <= words.length <= 100
// 1 <= words[i].length <= 100
// words[i] consists of lowercase English letters.

public class Solution {
    public IList<string> CommonChars(string[] words) {
        int[] minFreq = new int[26];
        Array.Fill(minFreq, Int32.MaxValue);
        foreach(var word in words){
            int[] freq = new int[26];
            foreach(char c in word)
                freq[c - 'a']++;
            for(int i = 0; i < 26; i++)
                minFreq[i] = Math.Min(minFreq[i], freq[i]);
        }
        IList<string> result = new List<string>();
        for(int i = 0; i < 26; i++){
            if(minFreq[i] < Int32.MaxValue){
                for(int j = 0; j < minFreq[i]; j++)
                    result.Add(((char)('a'+i)).ToString());
            }
        }
        return result;
    }
}