18/main.go

@@ -1,180 +0,0 @@
-package main
-
-import (
-	"bufio"
-	"fmt"
-	"os"
-	"strings"
-	"time"
-)
-
-func main() {
-	start := time.Now()
-	partOne()
-	duration := time.Since(start)
-	partTwo()
-	duration2 := time.Since(start)
-	fmt.Printf("p1: %s, p2: %s\n", duration, duration2-duration)
-}
-
-// an expression is a list of expressions and a list of operators that intersperse those expressions, OR a number.
-// as a sanity check, the length of the body list should always be one more than operators, unless both are 0,
-// in which case number must be set. Luckily, we don't have to worry about 0 (the "empty" state for numbers).
-type expression struct {
-	body      []expression
-	operators []op
-	number    int
-}
-
-// op can be one of two things.
-type op struct {
-	plus     bool
-	multiply bool
-}
-
-// 1 + 2 should parse to
-// expression{
-// 		body:[
-// 			expression{number: 1},
-// 			expression{number: 2},
-// 		],
-// 		operators:[
-// 			op{plus: true},
-// 		],
-// }
-
-// (2 * 2) + 2 should parse to:
-// expression{
-// 		body:[
-// 			expression{
-// 				body: [
-// 					expression{number: 2},
-// 					expression{number: 2},
-// 				],
-// 				operators: [
-// 					op{multiply: true},
-// 				],
-// 			},
-// 			expression{number: 2},
-// 		],
-// 		operators:[
-// 			op{plus:true}
-// 		]
-// }
-
-func parseExpression(e expression, s string) (expression, string) {
-	for i := 0; i < len(s); {
-		switch s[i] {
-		case '(':
-			sub, remainder := parseExpression(expression{}, s[i+1:])
-			e.body = append(e.body, sub)
-			i = len(s) - len(remainder) + 1 // skip everything we just parsed in the subexpression
-		case ')':
-			return e, s[i:]
-		case '*':
-			e.operators = append(e.operators, op{multiply: true})
-			i = i + 1
-		case '+':
-			e.operators = append(e.operators, op{plus: true})
-			i = i + 1
-		case ' ':
-			i = i + 1
-		case '1', '2', '3', '4', '5', '6', '7', '8', '9':
-			// luckily, it's all single-digit numbers and I don't need to track parser state
-			// an ASCII byte number minus the rune value of 0 equals the integer itself: '1' - '0' == 49 - 48;
-			// rune math returns a platform-specific int, so cast to generic int.
-			e.body = append(e.body, expression{number: int(s[i] - '0')})
-			i = i + 1
-		}
-	}
-	return e, ""
-}
-
-func printExpression(e expression) string {
-	result := ""
-	for i := 0; i < len(e.body); i = i + 1 {
-		if e.body[i].number != 0 {
-			result = result + fmt.Sprintf("%d ", e.body[i].number)
-		} else {
-			result = result + "(" + printExpression(e.body[i]) + ") "
-		}
-		if i < len(e.operators) {
-			if e.operators[i].multiply {
-				result = result + "* "
-			} else if e.operators[i].plus {
-				result = result + "+ "
-			}
-		}
-	}
-	return strings.TrimSpace(result)
-}
-
-// evaluation starts at the root then descends into the sub-expressions.
-func evalLeftToRight(e expression) int {
-	var result int
-	if e.number != 0 {
-		result = e.number
-	} else {
-		result = evalLeftToRight(e.body[0])
-	}
-	for i := 0; i < len(e.operators); i = i + 1 {
-		if e.operators[i].multiply {
-			result = result * evalLeftToRight(e.body[i+1])
-		}
-		if e.operators[i].plus {
-			result = result + evalLeftToRight(e.body[i+1])
-		}
-	}
-	return result
-}
-
-// previous approach might not work...
-func evalPlusThenMultiplication(e expression) int {
-	var result int
-	if e.number != 0 {
-		result = e.number
-	} else {
-		result = evalPlusThenMultiplication(e.body[0])
-	}
-	for i := 0; i < len(e.operators); i = i + 1 {
-		if e.operators[i].multiply {
-			result = result * evalPlusThenMultiplication(e.body[i+1])
-		}
-		if e.operators[i].plus {
-			result = result + evalPlusThenMultiplication(e.body[i+1])
-		}
-	}
-	return result
-}
-
-func partOne() {
-	f, _ := os.Open("input")
-	reader := bufio.NewReader(f)
-	scanner := bufio.NewScanner(reader)
-
-	total := 0
-
-	for scanner.Scan() {
-		line := scanner.Text()
-		e, _ := parseExpression(expression{}, line)
-		total = total + evalLeftToRight(e)
-	}
-
-	fmt.Println(total)
-}
-
-func partTwo() {
-	f, _ := os.Open("testinput")
-	reader := bufio.NewReader(f)
-	scanner := bufio.NewScanner(reader)
-
-	total := 0
-
-	for scanner.Scan() {
-		line := scanner.Text()
-		e, _ := parseExpression(expression{}, line)
-		fmt.Println(printExpression(e), "=", evalPlusThenMultiplication(e))
-	}
-
-	fmt.Println(total)
-}