Added solutions for 17th day: target practice

2021/17/example

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

2021/17/first.go

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+package main
+
+import (
+	"bufio"
+	"fmt"
+	"os"
+	"strconv"
+	"strings"
+)
+
+type vector struct {
+	x, y int
+}
+
+func main() {
+	scanner := bufio.NewScanner(os.Stdin)
+	scanner.Scan()
+	line := scanner.Text()
+	elts := strings.Split(line, "..")
+	eltsx1 := strings.Split(elts[0], "=")
+	x1, _ := strconv.Atoi(eltsx1[1])
+	eltsx2 := strings.Split(elts[1], ",")
+	x2, _ := strconv.Atoi(eltsx2[0])
+	eltsy1 := strings.Split(elts[1], "=")
+	y1, _ := strconv.Atoi(eltsy1[1])
+	y2, _ := strconv.Atoi(elts[2])
+
+	// We need to calculate which steps and horizontal speeds can hit the target box
+	x := 0
+	vx := 0 // its a vx max more than a vx
+	i := 1
+	for {
+		if x+vx+1 <= x2 {
+			vx += 1
+			x += vx
+			i++
+		} else {
+			break
+		}
+	}
+
+	hmax := 0
+	for nextVy := 0; nextVy < 10000; nextVy++ {
+		y := 0
+		vy := nextVy
+		tmpHmax := 0
+		j := 0
+		for {
+			if y+vy >= y1 {
+				y += vy
+				vy--
+				j++
+			} else {
+				break
+			}
+			if tmpHmax < y {
+				tmpHmax = y
+			}
+		}
+		if y >= y1 && y <= y2 && hmax < tmpHmax {
+			hmax = tmpHmax
+			fmt.Printf("h=%d, y=%d, vy=%d, j=%d\n", hmax, y, nextVy, j)
+		}
+	}
+
+	fmt.Printf("x1=%d, x2=%d, y1=%d, y2=%d\n", x1, x2, y1, y2)
+	fmt.Printf("i=%d, x=%d, vx=%d\n", i, x, vx)
+	fmt.Println(hmax)
+}

2021/17/input

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+target area: x=265..287, y=-103..-58

2021/17/second.go

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+package main
+
+import (
+	"bufio"
+	"fmt"
+	"os"
+	"strconv"
+	"strings"
+)
+
+type vector struct {
+	x, y int
+}
+
+func main() {
+	scanner := bufio.NewScanner(os.Stdin)
+	scanner.Scan()
+	line := scanner.Text()
+	elts := strings.Split(line, "..")
+	eltsx1 := strings.Split(elts[0], "=")
+	x1, _ := strconv.Atoi(eltsx1[1])
+	eltsx2 := strings.Split(elts[1], ",")
+	x2, _ := strconv.Atoi(eltsx2[0])
+	eltsy1 := strings.Split(elts[1], "=")
+	y1, _ := strconv.Atoi(eltsy1[1])
+	y2, _ := strconv.Atoi(elts[2])
+
+	possible := 0
+	for nextVx := 0; nextVx <= x2; nextVx++ {
+	out:
+		for nextVy := y1; nextVy < 1000; nextVy++ {
+			vx := nextVx
+			vy := nextVy
+			x := 0
+			y := 0
+			for {
+				if x >= x1 && x <= x2 && y >= y1 && y <= y2 {
+					possible++
+					continue out
+				}
+				if x > x2 || y < y1 {
+					break
+				}
+				if vx >= 0 {
+					x += vx
+					vx--
+				}
+				y += vy
+				vy--
+			}
+		}
+	}
+	fmt.Println(possible)
+}