advent_of_code_2024/day_07/solution.go

package day_07

import (
	"math"
	"strconv"
	"strings"
)

type Operator int

const (
	ADD      = iota
	MULTIPLY = iota
	CONCAT   = iota
)

type Equation struct {
	Result    int
	Variables []int
}

// task:https://adventofcode.com/2024/day/7
func SolveBasic(input string) int {
	equations := loadEquations(input)

	sum := 0
	for _, equation := range equations {
		if Solvable(equation, 2) {
			sum += equation.Result
		}
	}
	return sum
}

func Solvable(equation Equation, operators int) bool {
	for i := 0; i < numberOfSolutions(equation, operators); i++ {
		if solvable(equation, operators, i) {
			return true
		}
	}
	return false
}

func numberOfSolutions(equation Equation, operators int) int {
	return int(math.Pow(float64(operators), float64(len(equation.Variables)-1)))
}

func solvable(equation Equation, operators int, options int) bool {
	sum := equation.Variables[0]

	for i := 0; i < len(equation.Variables)-1; i++ {
		if sum > equation.Result {
			return false
		}
		operator := options % operators
		options = options / operators

		switch operator {
		case ADD:
			sum += equation.Variables[i+1]
		case MULTIPLY:
			sum *= equation.Variables[i+1]
		case CONCAT:
			offset := findLarger(equation.Variables[i+1])
			sum *= offset
			sum += equation.Variables[i+1]
		}
	}
	return sum == equation.Result
}

func findLarger(val int) int {
	larger := 10
	for val >= larger {
		larger *= 10
	}
	return larger
}

// task:https://adventofcode.com/2024/day/7#part2
func SolveComplex(input string) int {
	equations := loadEquations(input)

	sum := 0
	for _, equation := range equations {
		if Solvable(equation, 3) {
			sum += equation.Result
		}
	}
	return sum
}

func loadEquations(input string) (equations []Equation) {
	lines := strings.Split(input, "\n")

	for _, line := range lines {
		equations = append(equations, loadEquation(line))
	}
	return
}

func loadEquation(line string) Equation {
	substrings := strings.Split(line, ": ")
	equation := Equation{
		Result: must(strconv.Atoi(substrings[0])),
	}
	for _, param := range strings.Split(substrings[1], " ") {
		equation.Variables = append(equation.Variables, must(strconv.Atoi(param)))
	}
	return equation
}

func must(val int, err error) int {
	if err != nil {
		panic(err)
	}
	return val
}