From 564d55c5d2c63c82e6b4691601e439e5a84f12bd Mon Sep 17 00:00:00 2001
From: Martin Ashby <martin@ashbysoft.com>
Date: Fri, 23 Dec 2022 16:40:35 +0000
Subject: day18 pt2

---
 src/day18.rs | 76 +++++++++++++++++++++++++++++++++++++++++++++++-------------
 1 file changed, 60 insertions(+), 16 deletions(-)

(limited to 'src')

diff --git a/src/day18.rs b/src/day18.rs
index 636b342..ffb25ad 100644
--- a/src/day18.rs
+++ b/src/day18.rs
@@ -1,8 +1,14 @@
-fn adjescent(p: &(usize,usize,usize)) -> Vec<(usize,usize,usize)> {
+fn adjescent(p: &(usize,usize,usize), mx:usize) -> Vec<(usize,usize,usize)> {
     let mut v = vec![];
-    v.push((p.0+1,p.1,p.2));
-    v.push((p.0,p.1+1,p.2));
-    v.push((p.0,p.1,p.2+1));
+    if p.0+1 < mx {
+        v.push((p.0+1,p.1,p.2));
+    }
+    if p.1+1 < mx {
+        v.push((p.0,p.1+1,p.2));
+    }
+    if p.2+1 < mx {
+        v.push((p.0,p.1,p.2+1));
+    }
     if p.0 > 0 {
         v.push((p.0-1,p.1,p.2));
     }
@@ -15,6 +21,31 @@ fn adjescent(p: &(usize,usize,usize)) -> Vec<(usize,usize,usize)> {
     v
 }
 
+#[derive(Debug,PartialEq)]
+enum State {Rock,Unknown,OutsideAir}
+
+fn mark_outside(grid: &mut Vec<Vec<Vec<State>>>, curr: &(usize,usize,usize), mx: usize) {
+    for cell in adjescent(curr, mx) {
+        if let State::Unknown = grid[cell.0][cell.1][cell.2] {
+            grid[cell.0][cell.1][cell.2] = State::OutsideAir;
+            mark_outside(grid, &cell, mx);
+        }
+    }
+}
+
+fn surface_area(grid: &Vec<Vec<Vec<State>>>, cubes: &Vec<(usize,usize,usize)>, mx: usize) -> usize {
+    let surface_area: usize = cubes.iter().map(|cube| {
+        let mut score = 6;
+        for p in adjescent(cube, mx) {
+            if let State::Rock = grid[p.0][p.1][p.2] {
+                score -= 1;
+            }
+        }
+        score
+    }).sum();
+    surface_area
+}
+
 pub fn run(input:String) {
     let cubes = input.lines()
     .map(|line| {
@@ -25,20 +56,33 @@ pub fn run(input:String) {
         (res[0], res[1], res[2])
     }).collect::<Vec<(usize,usize,usize)>>();
     let mx: usize = cubes.iter().map(|t| {vec![t.0, t.1, t.2]}).flatten().max().unwrap() + 3;
-    // Allocate a 3d space..
-    let mut grid: Vec<Vec<Vec<bool>>> = (0..mx).map(|_| {(0..mx).map(|_| {(0..mx).map(|_| {false}).collect()}).collect()}).collect();
+    // Allocate a 3d space, and mark the rocky cubes
+    let mut grid: Vec<Vec<Vec<State>>> = (0..mx).map(|_| {(0..mx).map(|_| {(0..mx).map(|_| {State::Unknown}).collect()}).collect()}).collect();
     for cube in cubes.iter() {
-        grid[cube.0][cube.1][cube.2] = true;
+        grid[cube.0][cube.1][cube.2] = State::Rock;
     }
-    // Now count cubes. Each contributes 6,minus number of connections
-    let surface_area: usize = cubes.iter().map(|cube| {
-        let mut score = 6;
-        for p in adjescent(cube) {
-            if grid[p.0][p.1][p.2] {
-                score -= 1;
+    // Now count cubes. Each contributes 6, minus number of adjescent rocky cubes
+    
+    println!("Day 18 pt1: {}", surface_area(&grid, &cubes, mx));
+    // So... how can I remove pockets of air to get the _outside_ surface area?
+    // ans; fill in the inside areas!
+    // pick a spot definitely on the outside;; iterate out until all the outside is marked.
+    // Anything remaining is pockets, fill it in, re-calculate the outside surface area.
+    grid[0][0][0] = State::OutsideAir;
+    mark_outside(&mut grid, &(0,0,0), mx);
+    // All remaining Unknown cells are air pockets, fill 'em in
+    for x in 0..mx {
+        for y in 0..mx {
+            for z in 0..mx {
+                match grid[x][y][z] {
+                    State::Unknown => {
+                        grid[x][y][z] = State::Rock;
+                    },
+                    _ => ()
+                };
             }
         }
-        score
-    }).sum();
-    println!("Day 18: {}", surface_area);
+    }
+    // recalculate the surface area
+    println!("Day 18 pt2: {}", surface_area(&grid, &cubes, mx));
 }
\ No newline at end of file
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