Day 7 solution

I will probably end up regretting this since I assume the "wait to be given an input from some other process before continuing execution" paradigm is going to come up again, but this part 2 goroutine+channel solution felt good (taking advantage of Go features) and made me happy, so I rolled with it.

days/07.go

@@ -0,0 +1,116 @@
+package days
+
+import (
+	"fmt"
+	"sync"
+
+	"parnic.com/aoc2019/utilities"
+)
+
+type Day07 struct {
+	program utilities.IntcodeProgram
+	amps    []utilities.IntcodeProgram
+}
+
+func (d *Day07) Parse() {
+	d.program = utilities.LoadIntcodeProgram("07p")
+	d.amps = make([]utilities.IntcodeProgram, 5)
+	for i := range d.amps {
+		d.amps[i] = d.program.Copy()
+	}
+}
+
+func (d Day07) Num() int {
+	return 7
+}
+
+func (d *Day07) Part1() string {
+	var highestVal int64
+	var highestSequence []int64
+
+	allSequences := utilities.GetPermutations([]int64{0, 1, 2, 3, 4})
+	for _, sequence := range allSequences {
+		if len(sequence) != len(d.amps) {
+			panic("input sequence does not match up to number of amplifiers")
+		}
+
+		input := int64(0)
+		var output int64
+		for i, amp := range d.amps {
+			amp.RunIn(func(step int) int64 {
+				if step == 1 {
+					return sequence[i]
+				} else if step == 2 {
+					return input
+				}
+
+				panic("hit more input instructions than expected")
+			}, func(val int64, state utilities.IntcodeProgramState) {
+				output = val
+			})
+
+			input = output
+		}
+
+		if output > highestVal {
+			highestVal = output
+			if highestSequence == nil {
+				highestSequence = make([]int64, len(sequence))
+			}
+			copy(highestSequence, sequence)
+		}
+	}
+
+	return fmt.Sprintf("Max thruster signal: %s%d%s (produced by %v)", utilities.TextBold, highestVal, utilities.TextReset, highestSequence)
+}
+
+func (d *Day07) Part2() string {
+	var highestVal int64
+	var highestSequence []int64
+
+	allSequences := utilities.GetPermutations([]int64{5, 6, 7, 8, 9})
+	for _, sequence := range allSequences {
+		if len(sequence) != len(d.amps) {
+			panic("input sequence does not match up to number of amplifiers")
+		}
+
+		inputs := make([]chan int64, len(d.amps))
+		for i := range d.amps {
+			d.amps[i].Reset()
+			inputs[i] = make(chan int64, 1)
+			inputs[i] <- sequence[i]
+		}
+
+		var finalOutput int64
+		var wg sync.WaitGroup
+		for i := range d.amps {
+			wg.Add(1)
+			go func(idx int) {
+				d.amps[idx].RunIn(func(step int) int64 {
+					input := <-inputs[idx]
+					return input
+				}, func(val int64, state utilities.IntcodeProgramState) {
+					finalOutput = val
+					inputIdx := idx + 1
+					if inputIdx == len(inputs) {
+						inputIdx = 0
+					}
+					inputs[inputIdx] <- val
+				})
+				wg.Done()
+			}(i)
+		}
+		inputs[0] <- 0
+		wg.Wait()
+
+		if finalOutput > highestVal {
+			highestVal = finalOutput
+			if highestSequence == nil {
+				highestSequence = make([]int64, len(sequence))
+			}
+			copy(highestSequence, sequence)
+		}
+	}
+
+	return fmt.Sprintf("Max thruster signal: %s%d%s (produced by %v)", utilities.TextBold, highestVal, utilities.TextReset, highestSequence)
+}