Even more clean up.

Removed duplicated code in the descend stage and moved it to different
functions. Also, range finders are no longer technically infinite, but
are assumed to be.

2018/loc.svg

@@ -32,10 +32,10 @@ z
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-       <use style="stroke:#000000;stroke-width:0.8;" x="60.305455" xlink:href="#md180c468f1" y="307.584"/>
+       <use style="stroke:#000000;stroke-width:0.8;" x="60.305455" xlink:href="#m7d08bf4d8b" y="307.584"/>
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@@ -71,7 +71,7 @@ z
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+       <use style="stroke:#000000;stroke-width:0.8;" x="195.578182" xlink:href="#m7d08bf4d8b" y="307.584"/>
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@@ -302,7 +302,7 @@ L -3.5 0
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+    <path clip-path="url(#pa0af5c901d)" d="M 73.832727 282.048 
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+    <path clip-path="url(#pa0af5c901d)" d="M 73.832727 295.488 
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+    <path clip-path="url(#pa0af5c901d)" d="M 73.832727 233.088 
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2018/src/day17.rs

@@ -1,12 +1,13 @@
+use std::collections::HashSet;
+use std::io::BufRead;
+use std::io::BufReader;
 use std::io::Read;
 
-use common::Solution;
-use std::collections::HashSet;
-use regex::Regex;
-use std::io::BufReader;
-use std::io::BufRead;
 use itertools::Itertools;
 use itertools::MinMaxResult;
+use regex::Regex;
+
+use common::Solution;
 
 type Coordinate = (usize, usize);
 
@@ -41,7 +42,7 @@ impl Day17 {
                     for y in a..=b {
                         self.clays.insert((fixed, y));
                     }
-                },
+                }
                 "y" => {
                     for x in a..=b {
                         self.clays.insert((x, fixed));
@@ -55,11 +56,35 @@ impl Day17 {
             MinMaxResult::MinMax(a, b) => {
                 self.ymin = *a;
                 self.ymax = *b;
-            },
+            }
             _ => panic!(),
         };
     }
 
+    fn support_end<T>(&mut self, center: usize, range: T, y: usize) -> (usize, bool)
+        where T: Iterator<Item=usize>
+    {
+        let mut prev = center;
+        for x in range {
+            let pos = (x, y);
+            if self.clays.contains(&pos) {
+                return (prev, true);
+            }
+
+            prev = x;
+            let below = (x, y + 1);
+            self.descend(below);
+            if !self.is_supported(&below) {
+                return (x, false);
+            }
+        }
+        unreachable!();
+    }
+
+    fn is_supported(&self, pos: &Coordinate) -> bool {
+        self.clays.contains(pos) || self.contained.contains(pos)
+    }
+
     fn descend(&mut self, pos: Coordinate) {
         let (x, y) = pos;
 
@@ -71,49 +96,16 @@ impl Day17 {
 
         self.descend(below);
 
-        if self.clays.contains(&below) || self.contained.contains(&below) {
-            let mut contained = true;
+        if self.is_supported(&below) {
+            let (right, right_contained) = self.support_end(x, (x + 1).., y);
+            let (left, left_contained) = self.support_end(x, (0..x).rev(), y);
 
-            let mut layer = vec![pos];
+            let range = (left..=right).map(|x| (x, y));
 
-            let mut nx = x + 1;
-            loop {
-                let npos = (nx, y);
-                if self.clays.contains(&npos) {
-                    break;
-                }
-                layer.push(npos);
-
-                let nbelow = (nx, y + 1);
-                self.descend(nbelow);
-                if !self.clays.contains(&nbelow) && !self.contained.contains(&nbelow) {
-                    contained = false;
-                    break;
-                }
-
-                nx += 1;
-            }
-            let mut nx = x - 1;
-            loop {
-                let npos = (nx, y);
-                if self.clays.contains(&npos) {
-                    break;
-                }
-                layer.push(npos);
-
-                let nbelow = (nx, y + 1);
-                self.descend(nbelow);
-                if !self.clays.contains(&nbelow) && !self.contained.contains(&nbelow) {
-                    contained = false;
-                    break;
-                }
-                nx -= 1;
-            }
-
-            if contained {
-                self.contained.extend(layer);
+            if left_contained && right_contained {
+                self.contained.extend(range);
             } else {
-                self.flowing.extend(layer);
+                self.flowing.extend(range);
             }
         } else {
             self.flowing.insert(pos);
@@ -127,9 +119,8 @@ impl Solution for Day17 {
 
         self.descend((500, 0));
 
-        let result = self.contained.iter()
-            .chain(self.flowing.iter())
-            .filter(|&&(_, y)| y >= self.ymin && y <= self.ymax).count();
+        let result = self.contained.len()
+            + self.flowing.len() - self.ymin;
         format!("{}", result)
     }
 
@@ -138,16 +129,14 @@ impl Solution for Day17 {
 
         self.descend((500, 0));
 
-        let result = self.contained.iter()
-            .filter(|&&(_, y)| y >= self.ymin && y <= self.ymax).count();
-        format!("{}", result)
+        format!("{}", self.contained.len())
     }
 }
 
 #[cfg(test)]
 mod tests {
-    use day17::Day17;
     use common::Solution;
+    use day17::Day17;
 
     const SAMPLE_INPUT: &[u8] = include_bytes!("samples/17.txt");
 
@@ -162,5 +151,4 @@ mod tests {
         let mut instance = Day17::new();
         assert_eq!("29", instance.part2(&mut SAMPLE_INPUT));
     }
-
 }