add day8

day8/antinode.go

@@ -0,0 +1,109 @@
+package main
+
+import (
+    "os"
+    "fmt"
+    "strings"
+)
+
+// data types
+type Point struct {
+    x int16
+    y int16
+}
+
+type Antenna struct {
+    point Point
+    freq  byte
+}
+
+// general util
+func check(e error) {
+    if e != nil { panic(e) }
+}
+
+func (p Point) Mul(scalar int) Point {
+    return Point { x: p.x * int16(scalar), y: p.y * int16(scalar) }
+}
+
+func (p Point) Add(other Point) Point {
+    return Point { x: p.x + other.x, y: p.y + other.y }
+}
+
+func (p Point) Sub(other Point) Point {
+    return Point { x: p.x - other.x, y: p.y - other.y }
+}
+
+func contains(arr []Point, p Point) bool {
+    for _, elem := range arr {
+        if elem == p { return true }
+    }
+    return false
+}
+
+func addNonDuplicate(arr []Point, p Point) []Point {
+    if contains(arr, p) { return arr
+    } else { return append(arr, p) }
+}
+
+func newAntennas(data string) []Antenna {
+    /* Reads the puzzle input, return a list of antenna structs.
+     */
+    antennas := make([]Antenna, 0, 100)
+
+    for y, line := range strings.Split(data, "\n") {
+        for x, char := range []byte(line) {
+            if char != '.' {
+                antennas = append(antennas, Antenna{ point: Point{x: int16(x), y: int16(y)}, freq: char })
+            }
+        }
+    }
+
+    return antennas
+}
+
+func antinodes(points [2]Point) [2]Point {
+    var nodes [2]Point
+
+    distance := points[0].Sub(points[1])
+    nodes[0] = points[0].Add(distance)
+    nodes[1] = points[1].Sub(distance)
+
+    return nodes
+}
+
+// main loop
+func main() {
+
+    // read in file
+    dat, err := os.ReadFile("data.txt")
+    check(err)
+    dat_str := strings.TrimSpace(string(dat))
+    
+    lines := strings.Split(dat_str, "\n")
+    height, width := int16(len(lines)), int16(len(lines[0]))
+    antennas := newAntennas(dat_str)
+    
+    pairs := make([][2]Point, 0)
+    for _, ant1 := range antennas {
+        for _, ant2 := range antennas {
+            if ant1.freq == ant2.freq && ant1.point != ant2.point {
+                pairs = append(pairs, [2]Point{ant1.point, ant2.point})
+            }
+        }
+    }
+
+    
+    nodes := make([]Point, 0, len(pairs) * 2)
+    for _, pair := range pairs {
+        ns := antinodes(pair)
+        if ns[0].x >= 0 && ns[0].x < width && ns[0].y >= 0 && ns[0].y < height {
+            nodes = addNonDuplicate(nodes, ns[0])
+        }
+        if ns[1].x >= 0 && ns[1].x < width && ns[1].y >= 0 && ns[1].y < height {
+            nodes = addNonDuplicate(nodes, ns[1])
+        }
+    }
+
+    fmt.Println(len(nodes))
+}