#include <bits/stdc++.h>

using namespace std;

//b是不是a的前缀
bool isPrefix(string a, string b) {
    if (b.size() > a.size()) return false;
    return a.substr(b.size()) == b;
}

//b是不是a的后缀
bool isSuffix(string a, string b) {
    if (b.size() > a.size()) return false;
    //substr(0,i) 从下标0开始，截取长度为i的子串
    return a.substr(a.size() - b.size()) == b;
}

//合并两个字符串,最短相连
string merge(string a, string b) {
    //遍历b字符串的所有前缀，看看a字符串是不是以这个前缀结尾
    string pre;
    for (int i = 1; i <= b.size(); i++) {
        pre = b.substr(0, i);
        if (isSuffix(a, pre))
            break;//一旦找到就退出，这样，就保证是找到了最短的相连
    }
    if (pre == b) return "";
    //拼接 substr(0,i) 从下标0开始，截取长度为i的子串
    return a + b.substr(pre.size());
}

int main() {
    string c = merge("beast", "astonish");
    cout << c << endl;

    c = merge("cheat", "tact");
    cout << c << endl;

    c = merge("cheat", "choose");
    cout << c << endl;

    c = merge("envelope", "envelope");
    cout << c << endl;

    c = merge("abababab", "abababc");
    cout << c << endl;

    c = merge("abababab", "abababab");
    cout << c << endl;

    return 0;
}