1002. Find Common Characters

題目敘述:

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.

class Solution {
public:
    vector<string> commonChars(vector<string>& words) {
        vector<int> last = count(words[0]);
        for (int i = 1; i < words.size(); i++) {
            last = intersection(last, count(words[i]));
        }
        
        vector<string> result;
        for (int i = 0; i < 26; i++) {
            while (last[i] > 0) {
                result.push_back(string(1, 'a' + i));
                last[i]--;
            }
        }
        
        return result;
    }
    
private:
    vector<int> count(const string& str) {
        vector<int> frequency(26, 0);
        for (char c : str) {
            frequency[c - 'a']++;
        }
        return frequency;
    }
    
    vector<int> intersection(const vector<int>& a, const vector<int>& b) {
        vector<int> t(26, 0);
        for (int i = 0; i < 26; i++) {
            t[i] = min(a[i], b[i]);
        }
        return t;
    }
};