Super-Optimized 2019 Day 2

2019/day02/main.go

@@ -18,7 +18,6 @@ func main() {
 	for _, v := range strings.FieldsFunc(inp, f) {
 		prog = append(prog, Atoi(v))
 	}
-	//part1(prog)
 	part2(prog)
 }
 
@@ -36,6 +35,31 @@ func part1(prog []int) {
 	}
 }
 
+func part2(prog []int) {
+	runProg := func(n, v int, prog []int) int {
+		progcpy := make([]int, len(prog))
+		copy(progcpy, prog)
+		progcpy[1] = n
+		progcpy[2] = v
+		for i := 0; i < len(progcpy); i += 4 {
+			switch progcpy[i] {
+			case 1:
+				progcpy[progcpy[i+3]] = add(progcpy[i+1], progcpy[i+2], progcpy)
+			case 2:
+				progcpy[progcpy[i+3]] = mult(progcpy[i+1], progcpy[i+2], progcpy)
+			case 99:
+				i = len(progcpy)
+			}
+		}
+		return progcpy[0]
+	}
+	target := 19690720
+	zeroVal := runProg(0, 0, prog)
+	nDiff := runProg(1, 0, prog) - zeroVal
+	vDiff := runProg(0, 1, prog) - zeroVal
+	fmt.Println(((target - zeroVal) / nDiff), ((target%nDiff)-(zeroVal%nDiff))/vDiff)
+}
+
 func slowestPart2(prog []int) {
 	for n := 0; n <= 99; n++ {
 		for v := 0; v <= 99; v++ {
@@ -108,16 +132,6 @@ func slowPart2(prog []int) {
 	}
 }
 
-func part2(prog []int) {
-	target := 19690720
-	zeroVal := 610685
-	n := (target - zeroVal) / 360000
-	target = target % 1000
-	zeroVal = zeroVal % 1000
-	v := target - zeroVal
-	fmt.Println("Answer:", (100*n + v))
-}
-
 func printState(prog []int) {
 	fmt.Println(prog)
 }