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d1/README.md

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+Advent of code 2024
+
+Day 1
+
+Usage:
+
+    rustc d1p1.rs
+    cat input.txt | ./d1p1
+
+Part 1:
+
+Parse each line into a pair of ints; store them in a pair of heaps.
+Convert heaps into sorted lists. Iterate through them together
+and find the absolute difference between each pair of numbers.
+
+Part 2:
+
+Parse each line into a pair of ints; store the first in an array,
+place the second into a map that accumulate the number of times
+a value is seen.
+
+Iterate through the array, adding the number times the number of
+times it was seen in the map.
+

d1/d1p1.rs

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+use std::collections::BinaryHeap;
+use std::io;
+
+fn main() -> io::Result<()> {
+    let mut l1 = BinaryHeap::<u64>::new();
+    let mut l2 = BinaryHeap::<u64>::new();
+    for line in io::stdin().lines() {
+        let line = line?;
+        let parts: Vec<&str> = line.trim().split_whitespace().collect();
+        let (n1, n2) = (parts[0], parts[1]);
+        l1.push(n1.parse().unwrap());
+        l2.push(n2.parse().unwrap());
+    }
+    let l1 = l1.into_sorted_vec();
+    let l2 = l2.into_sorted_vec();
+    let mut sum = 0;
+    for (n1, n2) in l1.into_iter().zip(l2.into_iter()) {
+        sum += n1.abs_diff(n2);
+    }
+    println!("{}", sum);
+    Ok(())
+}

d1/d1p1.txt

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+3   4
+4   3
+2   5
+1   3
+3   9
+3   3

d1/d1p2.rs

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+use std::collections::HashMap;
+use std::io;
+
+fn main() -> io::Result<()> {
+    let mut l1: Vec<u64> = vec!();
+    let mut l2: HashMap<u64, u64> = HashMap::default();
+    for line in io::stdin().lines() {
+        let line = line?;
+        let parts: Vec<&str> = line.trim().split_whitespace().collect();
+        let (n1, n2) = (parts[0], parts[1]);
+        l1.push(n1.parse().unwrap());
+        let v = l2.entry(n2.parse::<u64>().unwrap()).or_insert(0);
+        *v += 1;
+    }
+    let mut sum = 0;
+    for n1 in l1.into_iter() {
+        sum += n1*l2.get(&n1).unwrap_or(&0);
+    }
+    println!("{}", sum);
+    Ok(())
+}