might be making a mistake starting 2018...

2019/day05/part1/main.go

@@ -0,0 +1,86 @@
+package main
+
+import (
+	"adventofcode/util"
+	"fmt"
+	"log"
+	"strconv"
+	"strings"
+)
+
+func main() {
+	// read the input file, modify it to a slice of numbers
+	inputFile := util.ReadFile("../input.txt")
+	splitStrings := strings.Split(inputFile, ",")
+
+	inputNumbers := make([]int, len(splitStrings))
+	for i, v := range splitStrings {
+		inputNumbers[i], _ = strconv.Atoi(v)
+	}
+
+	input := 1
+	step(inputNumbers, 0, input)
+}
+
+// step will read the next 4 values in the input `sli` and make updates
+// according to the opcodes
+func step(sli []int, index, input int) int {
+	// read the instruction, opcode and the indexes where the params point to
+	opcode, paramIndexes := getOpCodeAndIndexes(sli, index)
+
+	var output, jump int
+	switch opcode {
+	// 99: Terminates program
+	case 99:
+		fmt.Println("Terminating")
+		return -1
+	case 1: // 1: Add next two paramIndexes, store in third
+		sli[paramIndexes[2]] = sli[paramIndexes[0]] + sli[paramIndexes[1]]
+		jump = 4
+	case 2: // 2: Multiply next two and store in third
+		sli[paramIndexes[2]] = sli[paramIndexes[0]] * sli[paramIndexes[1]]
+		jump = 4
+	case 3: // 3: Takes one input and saves it to position of one parameter
+		sli[paramIndexes[0]] = input
+		jump = 2
+	case 4: // 4: outputs its input value
+		output = sli[paramIndexes[0]]
+		fmt.Printf("Opcode 4 output: %v\n", output)
+		jump = 2
+	default:
+		log.Fatal("Error: unknown opcode: ", opcode)
+	}
+	// recursively call itself & jump index value...
+	return step(sli, index+jump, output)
+}
+
+/*
+getOpCodeAndIndexes will parse the instruction at sli[index]
+- opcode will be the left two digits, mod by 100 will get that
+- rest of instructions will be grabbed via mod 10
+	- these also have to be parsed for the
+*/
+func getOpCodeAndIndexes(sli []int, index int) (int, [3]int) {
+	instruction := sli[index]
+
+	// opcode is the lowest two digits, so mod by 100
+	opcode := instruction % 100
+	instruction /= 100
+
+	// assign the indexes that need to be read by reading the parameter modes
+	var paramIndexes [3]int
+	for i := 1; i <= 3 && index+i < len(sli); i++ {
+		// grab the mode with a mod, last digit
+		mode := instruction % 10
+		instruction /= 10
+
+		switch mode {
+		case 1: // immediate mode, the index itself
+			paramIndexes[i-1] = index + i
+		case 0: // position mode, index will be the value at the index
+			paramIndexes[i-1] = sli[index+i]
+		}
+	}
+
+	return opcode, paramIndexes
+}