From 14d2607863d653b6b367e76955bbdde085340738 Mon Sep 17 00:00:00 2001
From: Justin Wernick <justin@worthe-it.co.za>
Date: Sat, 18 Dec 2021 21:05:52 +0200
Subject: Day 17

---
 inputs/day_17.txt |  1 +
 src/bin/day_17.rs | 82 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 83 insertions(+)
 create mode 100644 inputs/day_17.txt
 create mode 100644 src/bin/day_17.rs

diff --git a/inputs/day_17.txt b/inputs/day_17.txt
new file mode 100644
index 0000000..039df20
--- /dev/null
+++ b/inputs/day_17.txt
@@ -0,0 +1 @@
+target area: x=206..250, y=-105..-57
diff --git a/src/bin/day_17.rs b/src/bin/day_17.rs
new file mode 100644
index 0000000..0d60240
--- /dev/null
+++ b/src/bin/day_17.rs
@@ -0,0 +1,82 @@
+use nom::{
+    bytes::complete::tag, character::complete::i32 as nom_i32, combinator::map, sequence::tuple,
+    IResult,
+};
+use std::fs;
+
+fn main() -> Result<(), Box<dyn std::error::Error>> {
+    let input = fs::read_to_string("inputs/day_17.txt")?;
+    let target = parse_target(&input).unwrap().1;
+
+    let max_y_throw = 0 - target.min_y - 1;
+    let max_height = max_y_throw * (max_y_throw + 1) / 2;
+    dbg!(max_height);
+
+    let min_y_throw = target.min_y;
+    let max_x_throw = target.max_x;
+    let min_x_throw = (2.0 * target.min_x as f32).sqrt() as i32;
+
+    let mut count = 0;
+    for x in min_x_throw..=max_x_throw {
+        for y in min_y_throw..=max_y_throw {
+            if simulate_throw(x, y, &target) {
+                count += 1;
+            }
+        }
+    }
+    dbg!(count);
+
+    Ok(())
+}
+
+fn simulate_throw(mut x_vel: i32, mut y_vel: i32, target: &TargetArea) -> bool {
+    let mut x_pos = 0;
+    let mut y_pos = 0;
+    loop {
+        x_pos += x_vel;
+        y_pos += y_vel;
+        if x_vel > 0 {
+            x_vel -= 1;
+        }
+        y_vel -= 1;
+        if x_pos >= target.min_x
+            && x_pos <= target.max_x
+            && y_pos >= target.min_y
+            && y_pos <= target.max_y
+        {
+            return true;
+        }
+        if x_pos > target.max_x || y_pos < target.min_y {
+            return false;
+        }
+    }
+}
+
+#[derive(Debug)]
+struct TargetArea {
+    min_x: i32,
+    max_x: i32,
+    min_y: i32,
+    max_y: i32,
+}
+
+fn parse_target(input: &str) -> IResult<&str, TargetArea> {
+    map(
+        tuple((
+            tag("target area: x="),
+            nom_i32,
+            tag(".."),
+            nom_i32,
+            tag(", y="),
+            nom_i32,
+            tag(".."),
+            nom_i32,
+        )),
+        |(_, min_x, _, max_x, _, min_y, _, max_y)| TargetArea {
+            min_x,
+            max_x,
+            min_y,
+            max_y,
+        },
+    )(input)
+}
-- 
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