2020 Day 18 Complete

2020/day18/main.go

@@ -0,0 +1,129 @@
+package main
+
+import (
+	"fmt"
+	"regexp"
+	"strings"
+
+	h "git.bullercodeworks.com/brian/adventofcode/helpers"
+)
+
+var rgx = regexp.MustCompile(`\([0-9\*\+ ]*\)`)
+
+const (
+	LtoR = iota
+	AthenM
+)
+
+func main() {
+	fmt.Println("# Day 17")
+	fmt.Println()
+	inp := h.StdinToStringSlice()
+	fmt.Println("## Part1\nAnswer:", sum(inp, LtoR))
+	fmt.Println("## Part2\nAnswer:", sum(inp, AthenM))
+}
+
+func sum(inp []string, algo int) int {
+	var ret int
+	for k := range inp {
+		ret = ret + solve(inp[k], algo)
+	}
+	return ret
+}
+
+func solve(inp string, algo int) int {
+	var total int
+	rs := rgx.FindString(inp)
+	if rs == "" {
+		// no parentheticals
+		total = evaluateLine(inp, algo)
+	} else {
+		for rs != "" {
+			repl := evaluateLine(rs[1:len(rs)-1], algo)
+			inp = strings.Replace(inp, rs, h.Itoa(repl), -1)
+			rs = rgx.FindString(inp)
+		}
+		total = evaluateLine(inp, algo)
+	}
+	return total
+}
+
+func evaluateLine(inp string, algo int) int {
+	switch algo {
+	case LtoR:
+		return evaluateLineLtoR(inp)
+	case AthenM:
+		return evaluateLineAthenM(inp)
+	}
+	return 0
+}
+
+func evaluateLineLtoR(inp string) int {
+	var cnt, total int
+	var op string
+	// No parentheticals
+	pts := strings.Split(inp, " ")
+	for k := range pts {
+		switch pts[k] {
+		case "*", "+":
+			op = pts[k]
+		default:
+			if cnt == 0 {
+				total = h.Atoi(pts[k])
+				cnt++
+			} else {
+				if op == "+" {
+					total = total + h.Atoi(pts[k])
+				} else {
+					total = total * h.Atoi(pts[k])
+				}
+			}
+		}
+	}
+	return total
+}
+
+func evaluateLineAthenM(inp string) int {
+	// First solve all addition
+	inp = evaluateLineAddition(inp)
+	inp = evaluateLineMultiplication(inp)
+	return h.Atoi(inp)
+}
+
+func evaluateLineAddition(inp string) string {
+	var newPts []string
+	for strings.Contains(inp, "+") {
+		pts := strings.Split(inp, " ")
+		for k := 0; k < len(pts); k++ {
+			if pts[k] == "+" {
+				newPts = pts[:k-1]
+				newPts = append(newPts, h.Itoa(h.Atoi(pts[k-1])+h.Atoi(pts[k+1])))
+				newPts = append(newPts, pts[k+2:]...)
+				inp = strings.Join(newPts, " ")
+				break
+			}
+		}
+	}
+	return inp
+}
+
+func evaluateLineMultiplication(inp string) string {
+	var newPts []string
+	for strings.Contains(inp, "*") {
+		pts := strings.Split(inp, " ")
+		for k := 0; k < len(pts); k++ {
+			if pts[k] == "*" {
+				newPts = pts[:k-1]
+				newPts = append(newPts, h.Itoa(h.Atoi(pts[k-1])*h.Atoi(pts[k+1])))
+				newPts = append(newPts, pts[k+2:]...)
+				inp = strings.Join(newPts, " ")
+				break
+			}
+		}
+	}
+	return inp
+}
+
+type Token struct {
+	SubTokens []Token
+}