symetric-4.js

function sym(...args) {
    return args.reduce( (a,b,i) => {
        const valoresA = a.filter(item => !b.find(aux=>aux===item));
        const valoresB = b.filter(item => !a.find(aux=>aux===item));
        return [...valoresA, ...valoresB]
    },[]);
}
  
console.log(sym([3, 3, 3, 2, 5], [2, 1, 5, 7], [3, 4, 6, 6])); //[1, 7, 4, 6, 6]