Longest common prefix ref: http://qiita.com/giwa/items/0102e19e14f756379bee

file0.txt

[

  "abcdefgh",

  "aefghijk",

  "abcefgh"
]

file1.cpp

string getPrefix(string a, string b){
    int l = min(a.size(), b.size());
    string r="";
    for (int i; i < l; i++){
        if (a[i] == b[i]){
            string t{a[i]};
            r = r + t;
        }
    }
    return r;
}

string longestCommonPrefix(vector<string> &A) {
    string r = A[0];
    for (int i = 1; i < A.size(); i++){
        r = getPrefix(r, A[i]);
    }
    return r;
}