From 8e2720c3e421674615eac29bf4c02528a53f2606 Mon Sep 17 00:00:00 2001
From: Rokas Puzonas <rokas.puz@gmail.com>
Date: Sat, 15 Jan 2022 03:20:12 +0200
Subject: [PATCH] feat: solve day 17 part 1 & 2

---
 input/17.txt |   1 +
 src/day17.rs | 102 +++++++++++++++++++++++++++++++++++++++++++++++++++
 src/main.rs  |   3 ++
 3 files changed, 106 insertions(+)
 create mode 100644 input/17.txt
 create mode 100644 src/day17.rs

diff --git a/input/17.txt b/input/17.txt
new file mode 100644
index 0000000..ae66f1f
--- /dev/null
+++ b/input/17.txt
@@ -0,0 +1 @@
+target area: x=29..73, y=-248..-194
diff --git a/src/day17.rs b/src/day17.rs
new file mode 100644
index 0000000..5d5d11d
--- /dev/null
+++ b/src/day17.rs
@@ -0,0 +1,102 @@
+
+pub struct Rect {
+    x0: i32, x1: i32,
+    y0: i32, y1: i32,
+}
+
+pub fn parse_input(input: &str) -> Rect {
+    let (x_part, y_part) = input.strip_suffix("\n")
+        .or(Some(input))
+        .unwrap()
+        .strip_prefix("target area: ")
+        .unwrap()
+        .split_once(", ")
+        .unwrap();
+    let (x0, x1) = x_part[2..].split_once("..").unwrap();
+    let (y0, y1) = y_part[2..].split_once("..").unwrap();
+    return Rect {
+        x0: x0.parse().unwrap(),
+        x1: x1.parse().unwrap(),
+        y0: y0.parse().unwrap(),
+        y1: y1.parse().unwrap()
+    }
+}
+
+fn sign(x: i32) -> i32 {
+    if x > 0 { 1 } else if x < 0 { -1 } else { 0 }
+}
+
+fn is_overshot(px: i32, py: i32, target: &Rect) -> bool {
+    px > target.x1 || py < target.y0
+}
+
+fn is_in_rect(px: i32, py: i32, target: &Rect) -> bool {
+    target.x0 <= px && px <= target.x1 &&
+    target.y0 <= py && py <= target.y1
+}
+
+fn simulate(target: &Rect, initial_vx: i32, initial_vy: i32) -> i32 {
+    let mut px = 0;
+    let mut py = 0;
+    let mut vx = initial_vx;
+    let mut vy = initial_vy;
+    let mut maxy = 0;
+
+    while !is_overshot(px, py, target) {
+        px += vx;
+        py += vy;
+
+        if is_in_rect(px, py, target) {
+            return maxy;
+        }
+        
+        maxy = maxy.max(py);
+
+        vx -= sign(vx);
+        vy -= 1;
+    }
+
+    return -1;
+}
+
+pub fn part1(target: &Rect) -> i32 {
+    let mut maxy = 0;
+    for vx in 0..target.x1 {
+        for vy in target.y0..-target.y0 {
+            maxy = maxy.max(simulate(target, vx, vy));
+        }
+    }
+    return maxy;
+}
+
+pub fn part2(target: &Rect) -> i32 {
+    let mut count = 0;
+    for vx in 0..=target.x1 {
+        for vy in target.y0..-target.y0 {
+            if simulate(target, vx, vy) >= 0 {
+                count += 1;
+            }
+        }
+    }
+    return count;
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn part1_example() {
+        let target = parse_input("target area: x=20..30, y=-10..-5");
+        let result = part1(&target);
+        assert_eq!(result, 45);
+    }
+
+    #[test]
+    fn part2_example() {
+        let target = parse_input("target area: x=20..30, y=-10..-5");
+        let result = part2(&target);
+        assert_eq!(result, 112);
+    }
+}
+
diff --git a/src/main.rs b/src/main.rs
index 21a6104..3fd5c79 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -14,6 +14,7 @@ mod day13;
 mod day14;
 mod day15;
 mod day16;
+mod day17;
 
 use std::{env, process};
 use std::fs::File;
@@ -62,6 +63,8 @@ fn run(day: i32, part: i32, input_filename: &str) {
         "15.2" => println!("{}", day15::part2(&mut day15::parse_input(&contents))),
         "16.1" => println!("{}", day16::part1(&day16::parse_input(&contents))),
         "16.2" => println!("{}", day16::part2(&day16::parse_input(&contents))),
+        "17.1" => println!("{}", day17::part1(&day17::parse_input(&contents))),
+        "17.2" => println!("{}", day17::part2(&day17::parse_input(&contents))),
         _ => println!("Day {} part {} not found", day, part)
     }
 }