add day 20 part 1 and a half WIP

day20/Cargo.lock

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+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 4
+
+[[package]]
+name = "day20"
+version = "0.1.0"

day20/Cargo.toml

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+[package]
+name = "day20"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]

day20/example.txt

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+5-8
+0-2
+4-7

day20/src/main.rs

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+use std::ops::RangeInclusive;
+
+#[cfg(debug_assertions)]
+const INPUT: &str = "example.txt";
+#[cfg(not(debug_assertions))]
+const INPUT: &str = "input.txt";
+
+fn main() {
+    let ranges: Vec<_> = std::fs::read_to_string(INPUT)
+        .unwrap()
+        .lines()
+        .map(|l| {
+            let mut parts = l.split('-');
+            let low = parts.next().unwrap();
+            let high = parts.next().unwrap();
+            RangeInclusive::new(low.parse::<usize>().unwrap(), high.parse().unwrap())
+        })
+        .collect();
+
+    // dbg!(&ranges);
+    let result = consolidate_all_ranges(&ranges);
+    dbg!(result);
+}
+
+fn consolidate_all_ranges(ranges: &[RangeInclusive<usize>]) -> Vec<RangeInclusive<usize>> {
+    let mut work = ranges.to_vec();
+
+    let mut to_remove = (0, 0);
+    loop {
+        let mut found = None;
+        'middle: loop {
+            if work.len() == 1 {
+                break;
+            }
+            for i in 0..work.len() - 1 {
+                for j in i + 1..work.len() {
+                    if let Some(range) = merge_two_ranges(&[ranges[i].clone(), ranges[j].clone()]) {
+                        found = Some(range);
+                        to_remove = (i, j);
+                        break 'middle;
+                    }
+                }
+            }
+        }
+        if let Some(range) = found {
+            dbg!(&range);
+            work.remove(to_remove.1);
+            work.remove(to_remove.0);
+            work.push(range);
+        } else {
+            break;
+        }
+    }
+
+    work
+}
+
+fn merge_two_ranges(ranges: &[RangeInclusive<usize>]) -> Option<RangeInclusive<usize>> {
+    let a = &ranges[0];
+    let b = &ranges[1];
+
+    if ranges_overlap(a, b) {
+        let start = if a.start() < b.start() {
+            a.start()
+        } else {
+            b.start()
+        };
+        let end = if a.end() > b.end() { a.end() } else { b.end() };
+        Some(*start..=*end)
+    } else {
+        None
+    }
+}
+
+fn ranges_overlap(a: &RangeInclusive<usize>, b: &RangeInclusive<usize>) -> bool {
+    (a.start() < b.start() && a.end() > b.start())
+        || (b.start() < a.start() && b.end() > a.start())
+        || (a.start() < b.start() && a.end() > b.end())
+        || (b.start() < a.start() && b.end() > a.end())
+}