[AcWing 770] 单词替换

#include
#include

using namespace std;
string s, a ,b;

int main()
{
    getline(cin ,s);
    cin >> a >> b;
    stringstream ssin(s);
    string str;
    while (ssin >> str) {
        if (str == a)   cout << b << ' ';
        else    cout << str << ' ';
    }
    return 0;
}