From 5bcc40b0305a92879cadf58a1907f4f6333fd9ae Mon Sep 17 00:00:00 2001
From: Joseph Montanaro <jfmonty2@gmail.com>
Date: Sun, 12 Dec 2021 21:55:21 -0800
Subject: [PATCH] day 9 part 1 (not working)

---
 2021/src/day9.rs | 105 +++++++++++++++++++++++++++++++++++++++++++++++
 2021/src/main.rs |   6 +--
 2 files changed, 108 insertions(+), 3 deletions(-)
 create mode 100644 2021/src/day9.rs

diff --git a/2021/src/day9.rs b/2021/src/day9.rs
new file mode 100644
index 0000000..90bcb96
--- /dev/null
+++ b/2021/src/day9.rs
@@ -0,0 +1,105 @@
+use color_eyre::eyre;
+use eyre::eyre;
+
+
+// #[derive(Eq, PartialEq)]
+enum Elevation {
+    High,
+    Mid,
+    Low,
+}
+use Elevation::*;
+
+
+fn load(data: &str) -> eyre::Result<Vec<Vec<u32>>> {
+    let mut heights = Vec::new();
+    for line in data.lines() {
+        let mut row = Vec::new();
+        for c in line.chars() {
+            match c.to_digit(10) {
+                Some(d) => row.push(d),
+                None => return Err(eyre!("Invalid character (not a digit): {}", c)),
+            }
+        }
+        heights.push(row);
+    }
+    Ok(heights)
+}
+
+
+fn cmp_horizontal(row: &[u32], pos: usize) -> Elevation {
+    let prev = if pos == 0 {None} else {Some(row[pos - 1])};
+    let next = if pos == row.len() - 1 {None} else {Some(row[pos + 1])};
+    let current = row[pos];
+
+    if current > prev.unwrap_or(0) && current > next.unwrap_or(0) {
+        High
+    }
+    else if current < prev.unwrap_or(9) && current < next.unwrap_or(9) {
+        Low
+    }
+    else {
+        Mid
+    }
+}
+
+
+fn scan(map: &[Vec<u32>]) -> Vec<Vec<Elevation>> {
+    let mut result: Vec<Vec<Elevation>> = Vec::new();
+    for (r, row) in map.iter().enumerate() {
+        let mut scanned_row = Vec::new();
+        for (col, height) in row.iter().enumerate() {
+            let elev = match cmp_horizontal(row, col) {
+                High => {
+                    if r == 0 || height > &map[r - 1][col] {
+                        High
+                    }
+                    else {
+                        Mid
+                    }
+                },
+                Low => {
+                    if r == 0 || height < &map[r - 1][col] {
+                        Low
+                    }
+                    else {
+                        Mid
+                    }
+                },
+                Mid => Mid,
+            };
+
+            if r > 0 {
+                let above = &result[r - 1][col];
+                if let (&High, &High) | (&Low, &Low) = (&elev, above) {
+                    result[r - 1][col] = Mid;
+                }
+            }
+            scanned_row.push(elev);
+        }
+        result.push(scanned_row);
+    }
+    result
+}
+
+
+fn part1(map: &[Vec<u32>], compares: &[Vec<Elevation>]) -> u32 {
+    let mut result = 0;
+    for (r, row) in compares.iter().enumerate() {
+        for (col, elev) in row.iter().enumerate() {
+            if let Low = elev {
+                result += map[r][col] + 1
+            }
+        }
+    }
+    result
+}
+
+
+pub fn run(data: &str) -> eyre::Result<(u32, u32)> {
+    let map = load(data)?;
+    let compares = scan(&map);
+
+    let one = part1(&map, &compares);
+    Ok((one, 0))
+}
diff --git a/2021/src/main.rs b/2021/src/main.rs
index 806623b..ece7b77 100644
--- a/2021/src/main.rs
+++ b/2021/src/main.rs
@@ -4,14 +4,14 @@ use color_eyre::eyre;
 
 mod lib;
 use lib::load;
-mod day8;
+mod day9;
 
 
 fn main() -> eyre::Result<()> {
-    let data = load("data/08.txt")?;
+    let data = load("data/09.txt")?;
 
     let start = Instant::now();
-    let (one, two) = day8::run(&data)?;
+    let (one, two) = day9::run(&data)?;
     let (dur, unit) = format_ns(start.elapsed().as_nanos());
 
     let precision = 2.0 - dur.log10().floor();