Here is my C++ solution :

string catAndMouse(int x, int y, int z) { int diffA = abs(z - x); int diffB = abs(z - y);

if(diffA < diffB)
{
    return "Cat A";
}
else if(diffB < diffA) 
{
    return "Cat B";
}
else {
    return "Mouse C";
}

}