LeetCode 1002. Find Common Characters

原题链接在这里：https://leetcode.com/problems/find-common-characters/

题目：

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

题解：

Find the minimum of frequency for each lowercase char in each of string.

Time Complexity: O(n*m). n = A.length. m is average length of string in A.

Space: O(1).

AC Java:

class Solution {
    public List<String> commonChars(String[] A) {
        List<String> res = new ArrayList<>();
        if(A == null || A.length == 0){
            return res;
        }
        
        int [] globalMap = new int[26];
        Arrays.fill(globalMap, Integer.MAX_VALUE);
        for(String s : A){
            int [] map = new int[26];
            for(int i = 0; i<s.length(); i++){
                map[s.charAt(i) - 'a']++;
            }
            
            for(int i = 0; i<26; i++){
                globalMap[i] = Math.min(globalMap[i], map[i]);
            }
        }
        
        for(int i = 0; i<26; i++){
            for(int j = 0; j<globalMap[i]; j++){
                res.add(""+ (char)('a' + i));
            }
        }
        
        return res;
    }
}

AC C++:

class Solution {
public:
    vector<string> commonChars(vector<string>& words) {
        vector<string> res;
        vector<int> global_map(26, INT_MAX);
        for(auto& word : words){
            vector<int> map(26, 0);
            for(auto& c : word){
                map[c - 'a']++;
            }

            for(int i = 0; i < 26; i++){
                global_map[i] = min(global_map[i], map[i]);
            }
        }

        for(int i = 0; i < 26; i++){
            for(int j = 0; j < global_map[i]; j++){
                res.push_back(string(1, 'a' + i));
            }
        }      

        return res;
    }
};

类似Intersection of Two Arrays II.