2021 Day 17 Complete

2021/day17/input

@@ -0,0 +1 @@
+target area: x=277..318, y=-92..-53

2021/day17/main.go

@@ -0,0 +1,62 @@
+package main
+
+import (
+	"fmt"
+
+	h "git.bullercodeworks.com/brian/adventofcode/helpers"
+)
+
+// Target Area
+var x1, y1, x2, y2 int
+
+func main() {
+	inp := h.StdinToString()
+	fmt.Sscanf(inp, "target area: x=%d..%d, y=%d..%d", &x1, &x2, &y1, &y2)
+
+	var maxy int
+	r := make(map[h.Coordinate]bool)
+	b := 500
+
+	for x := b * -1; x < b; x++ {
+		for y := b * -1; y < b; y++ {
+			v := h.Coordinate{X: x, Y: y}
+			if m, ok := testForHit(h.Coordinate{}, v); ok {
+				if m > maxy {
+					maxy = m
+				}
+				r[v] = true
+			}
+		}
+	}
+	fmt.Println("Maximum Peak:", maxy)
+	fmt.Println("Valid Velocities:", len(r))
+}
+
+func testForHit(pos h.Coordinate, vel h.Coordinate) (int, bool) {
+	var maxy int
+	for {
+		pos.X += vel.X
+		pos.Y += vel.Y
+		if pos.Y > maxy {
+			maxy = pos.Y
+		}
+		if pos.X >= x1 && pos.X <= x2 && pos.Y >= y1 && pos.Y <= y2 {
+			return maxy, true
+		}
+		if vel.X == 0 && vel.Y < y1 {
+			return maxy, false
+		}
+		if vel.X > 0 {
+			vel.X--
+		}
+		if vel.X < 0 {
+			vel.X++
+		}
+		vel.Y--
+	}
+}
+
+type xy struct {
+	x int
+	y int
+}

2021/day17/testinput

@@ -0,0 +1 @@
+target area: x=20..30, y=-10..-5