Add Day05 - part 2

AoC_2025/src/days/day05.rs

@@ -1,4 +1,4 @@
-use std::collections::BTreeSet;
+use std::cmp::max;
 
 use crate::days::Solution;
 
@@ -50,6 +50,64 @@ impl Solution for Day05 {
             ingredients: _,
         }: &Self::Input,
     ) -> usize {
-        0
+        reduce_ranges(&ranges).iter().map(|(x, y)| y + 1 - x).sum()
     }
 }
+
+/// Reduce recursively a Vec of ranges to a Vec of non-overlapping ranges
+fn reduce_ranges(input: &Vec<(usize, usize)>) -> Vec<(usize, usize)> {
+    let mut input = input.clone();
+    input.sort();
+    let mut input = group_overlapping_ranges(&input);
+
+    input
+        .iter_mut()
+        .flat_map(|g| {
+            if g.len() > 1 {
+                reduce_ranges(
+                    &g.chunks(2)
+                        .flat_map(|w| {
+                            if w.len() == 2 {
+                                simplify_ranges(w[0], w[1])
+                            } else {
+                                vec![w[0]]
+                            }
+                        })
+                        .collect(),
+                )
+            } else {
+                g.to_owned()
+            }
+        })
+        .collect()
+}
+
+/// Simplify two ordered ranges (p1 <= p2) to give an equivalent Vec of disctinct ranges
+fn simplify_ranges((x1, y1): (usize, usize), (x2, y2): (usize, usize)) -> Vec<(usize, usize)> {
+    if y1 < x2 {
+        vec![(x1, y1), (x2, y2)]
+    } else if (x1, y1) == (x2, y2) {
+        vec![(x1, y1)]
+    } else if y1 == x2 {
+        vec![(x1, y2)]
+    } else {
+        vec![(x1, max(y1, y2))]
+    }
+}
+
+/// Group a Vec of ranges by overlapping ranges
+fn group_overlapping_ranges(ranges: &Vec<(usize, usize)>) -> Vec<Vec<(usize, usize)>> {
+    ranges
+        .iter()
+        .fold((vec![], None), |(mut v, state), &(x, y)| {
+            if state.is_none_or(|(_, sy)| sy < x) {
+                // Create new range group
+                v.push(vec![(x, y)]);
+                (v, Some((x, y)))
+            } else {
+                v.last_mut().unwrap().push((x, y));
+                (v, Some((x, max(y, state.unwrap().1))))
+            }
+        })
+        .0
+}