This is my CPP solution.
class Solution {
public:
vector<string> commonChars(vector<string>& A) {
int n = A.size();
vector<int> f(26,0);
for(int i=0;i<26;i++)
f[i] = count(A[0].begin(),A[0].end(),i+'a');
for(int i=1;i<n;i++)
for(int j=0;j<26;j++){
int f_chr = count(A[i].begin(),A[i].end(),j+'a');
f[j] = min(f[j],f_chr);
}
vector<string> res;
for(int i=0;i<26;i++){
while(f[i]--){
string str;
str.push_back(i+'a');
res.push_back(str);
}
}
return res;
}
};