advent-of-code-go/2019/day10/part1/main.go

package main

import (
	"github.com/alexchao26/advent-of-code-go/util"
	"fmt"
	"strings"
)

func main() {
	// need to read the input.txt file and split each line into a slice
	input := util.ReadFile("../input.txt")
	stringSlice := strings.Split(input, "\n")

	// split into a 2D grid with each character
	gridSlice := make([][]string, len(stringSlice))
	for i, str := range stringSlice {
		gridSlice[i] = strings.Split(str, "")
	}

	// will be the final result value
	var result int
	var finalCoords [2]int
	// iterate through entire slice, for each asteroid found, call a helper function
	for rowIndex, rowSlice := range gridSlice {
		for colIndex, element := range rowSlice {
			if element == "#" {
				// # are "asteroids", . are empty space
				// helper function will return how many asteroids are "findable" from the current asteroid
				visibleFromElement := visibleFromAsteroid(gridSlice, rowIndex, colIndex)

				// take max of return of helper function at end of each loop
				if result < visibleFromElement {
					result = visibleFromElement
					finalCoords[0], finalCoords[1] = rowIndex, colIndex
				}
			}
		}
	}

	// print out the max found
	fmt.Printf("best asteroid for the station: row[%v] col[%v]\n", finalCoords[0], finalCoords[1]) // [13, 11]
	fmt.Println("from 13, 11 (y, x)", result)
}

// helper function will take, x and y coordinates, and the 2D slice
// will create a two maps of floats to booleans
//     (one map to cover left side of asteroid, one map to cover right side of asteroid)
//     so that anything that is blocked will not be double counted
// and edge case handling for planets vertically above or below the current asteroid
func visibleFromAsteroid(grid [][]string, row, col int) (result int) {
	// make the two maps
	leftMap, rightMap := make(map[float64]bool), make(map[float64]bool)
	// make the two booleans for up and down. zero value is false
	var upBool, downBool bool

	// iterate through every element of the grid slices
	for rowIndex, rowSlice := range grid {
		for colIndex, element := range rowSlice {
			// NOTE this control flow is _GROSS_. Better solution in part2 solution
			// ensure element is an asteroid & not the asteroid that the helper function is being run on
			if element == "#" && !(row == rowIndex && col == colIndex) {
				rise := rowIndex - row
				run := colIndex - col

				// handle if the found asteroid is directly above the inputted row/col asteroid
				if run == 0 {
					if rise < 0 {
						// check down
						// note that up and down are semantically "flipped" due to the 2 row being "above" the 0 row
						if !downBool {
							downBool = true
							result++
						}
					} else {
						if !upBool {
							upBool = true
							result++
						}
					}
				} else {
					slope := float64(rise) / float64(run)
					// handle left or right map
					if run < 0 {
						// leftMap
						if _, inLeftMap := leftMap[slope]; !inLeftMap {
							leftMap[slope] = true
							result++
						}
					} else {
						// rightMap
						if _, inRightMap := rightMap[slope]; !inRightMap {
							rightMap[slope] = true
							result++
						}
					}
				}
			}
		}
	}

	return result
}