难度不大，考虑用$map$做。 直接给出AC Code

#include <bits/stdc++.h>
using namespace std;
#define int long long
const int N = 1e4 + 5;
int n;
map<string, string> m;
string s, ans;
signed main() {
    cin >> n;
    for (int i = 1; i <= n; i++) {
        string a, b;
        cin >> a >> b;
        m[a] = b;
    }
    cin >> s;
    s += '.';
    string t = "";
    for (char c : s) {
        if (c >= 'a' && c <= 'z')
            t += c;
        else {
            if (t != "") {
                if (m.count(t))
                    ans += m[t];
                else
                    ans += "UNK";
                t = "";
            }
            ans += c;
        }
        // cout<<c<<" "<<ans<<" "<<t<<endl;
    }
    ans.pop_back();
    cout << ans << endl;
    return 0;
}