Intersect 交集，Except 差集，Union 并集
int[] oldArray = { , , , ,  };

int[] newArray = { , , , , ,  };

var jiaoJi = oldArray.Intersect(newArray).ToList();//2,4,5

var oldChaJi = oldArray.Except(newArray).ToList();//1,3

var newChaJi = newArray.Except(oldArray).ToList();//7,8,9

var bingJi = oldArray.Union(newArray).ToList();//1,2,3,4,5,7,8,9