A computer-implemented method, a machine learning system, and non-transitory computer-readable storage medium for designing electrical circuits are provided. In the method input data, comprising an indication of a plurality of connections including a first and second connection is processed to generate a representation of the electrical circuit. Routes for the first and second connections are determined using an iterative process that includes defining one or more orders in which to determine routes for the first and second connections. A Sequential Monte Carlo process is used to perform a look ahead search of each defined order by generating simulations in respect of routes to be determined for the connections in the orders, the Sequential Monte Carlo process being guided by a neural network. A connection is selected and a route for the selected connection is determined. The representation is updated by providing an action selection signal representing the determined route.