day7.cs

var phaseSetting = new int[] { 0, 1, 2, 3, 4 };
var maxThrusters = UInt64.MinValue;

do {
    var vms = phaseSetting
        .Select(x => new Intcode((int[])memory.Clone(), x.ToString()))
        .ToArray();

    var signal = "0";
    while (!vms.Last().HasFinished) {
        foreach (var vm in vms) {
            signal = vm.Run(signal);
        }
    }

    maxThrusters = Math.Max(UInt64.Parse(signal), maxThrusters);
} while (Permutations.NextPermutation(phaseSetting));