From 7b80c47dfc7c3718fe3dbde9aa09a9ba752ab40c Mon Sep 17 00:00:00 2001
From: =?utf8?q?Gr=C3=A9gory=20Burri?= <gregory.burri@matisa.ch>
Date: Thu, 5 Dec 2019 13:07:44 +0100
Subject: [PATCH] Day03 - part2

---
 src/day03.rs | 76 +++++++++++++++++++++++++++++++++++++++++-----------
 src/main.rs  |  5 ++--
 2 files changed, 64 insertions(+), 17 deletions(-)

diff --git a/src/day03.rs b/src/day03.rs
index a35ce3f..808f6f9 100644
--- a/src/day03.rs
+++ b/src/day03.rs
@@ -1,37 +1,56 @@
 use std::iter::Iterator;
+use std::iter::FromIterator;
 use std::collections::HashSet;
+use std::collections::HashMap;
 
 pub fn split_movements(movements: &str) -> Vec<&str> {
     movements.split(',').collect()
 }
 
-pub fn manhattan_distance_from_cross_to_port(wire1: &[&str], wire2: &[&str]) -> i32 {
-    fn positions(wire: &[&str]) -> HashSet<(i32, i32)> {
-        let (mut x, mut y) = (0, 0);
-        let mut pos = HashSet::<(i32, i32)>::new();
-        for mov in wire {
-            let distance = mov[1..].parse::<i32>().unwrap();
-            match mov.chars().nth(0).unwrap() {
-                'U'      => { for y2 in y+1 ..= y + distance { pos.insert((x, y2)); } y += distance },
-                'D'      => { for y2 in y - distance .. y    { pos.insert((x, y2)); } y -= distance },
-                'R'      => { for x2 in x+1 ..= x + distance { pos.insert((x2, y)); } x += distance },
-                'L' | _  => { for x2 in x - distance .. x    { pos.insert((x2, y)); } x -= distance },
-            }
+fn positions(wire: &[&str]) -> Vec<(i32, i32)> {
+    let (mut x, mut y) = (0, 0);
+    let mut pos = Vec::<(i32, i32)>::new();
+    for mov in wire {
+        let distance = mov[1..].parse::<i32>().unwrap();
+        match mov.chars().nth(0).unwrap() {
+            'U'      => { for y2 in  y+1 ..= y + distance     { pos.push((x, y2)); } y += distance },
+            'D'      => { for y2 in (y - distance .. y).rev() { pos.push((x, y2)); } y -= distance },
+            'R'      => { for x2 in  x+1 ..= x + distance     { pos.push((x2, y)); } x += distance },
+            'L' | _  => { for x2 in (x - distance .. x).rev() { pos.push((x2, y)); } x -= distance },
         }
-        pos
     }
+    pos
+}
 
-    let (positions_wire1, positions_wire2) = (positions(wire1), positions(wire2));
+pub fn manhattan_distance_from_cross_to_port(wire1: &[&str], wire2: &[&str]) -> i32 {
+    let positions_wire1: HashSet<(i32, i32)> = HashSet::from_iter(positions(wire1));
+    let positions_wire2: HashSet<(i32, i32)> = HashSet::from_iter(positions(wire2));
     let cross: HashSet<_> = positions_wire1.intersection(&positions_wire2).collect();
     cross.iter().map(|(x, y)| x.abs() + y.abs()).min().unwrap()
 }
 
+pub fn first_cross_sum_of_lengths(wire1: &[&str], wire2: &[&str]) -> usize {
+    let positions_wire1 = positions(wire1);
+    let positions_wire1_indexed: HashMap<&(i32, i32), usize> = HashMap::from_iter(positions_wire1.iter().enumerate().map(|(i, pos)| (pos, i)).rev());
+
+    positions(wire2)
+        .iter().enumerate().filter_map(
+            |(j, pos2)| {
+                if let Some (i) = positions_wire1_indexed.get(pos2) {
+                    Some (j + i + 2)
+                } else {
+                    None
+                }
+            }
+        ).min().unwrap()
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
 
     #[test]
-    fn simple_cases() {
+    fn part1() {
         assert_eq!(
             manhattan_distance_from_cross_to_port(
                 &split_movements("R8,U5,L5,D3"),
@@ -56,4 +75,31 @@ mod tests {
             135
         );
     }
+
+    #[test]
+    fn part2() {
+        assert_eq!(
+            first_cross_sum_of_lengths(
+                &split_movements("R8,U5,L5,D3"),
+                &split_movements("U7,R6,D4,L5")
+            ),
+            30
+        );
+
+        assert_eq!(
+            first_cross_sum_of_lengths(
+                &split_movements("R75,D30,R83,U83,L12,D49,R71,U7,L72"),
+                &split_movements("U62,R66,U55,R34,D71,R55,D58,R83")
+            ),
+            610
+        );
+
+        assert_eq!(
+            first_cross_sum_of_lengths(
+                &split_movements("R98,U47,R26,D63,R33,U87,L62,D20,R33,U53,R51"),
+                &split_movements("U98,R91,D20,R16,D67,R40,U7,R15,U6,R7")
+            ),
+            410
+        );
+    }
 }
\ No newline at end of file
diff --git a/src/main.rs b/src/main.rs
index eff33ed..b508728 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -21,8 +21,9 @@ fn day03() -> String {
     let file_content = fs::read_to_string("data/day03.input").unwrap();
     let movements: Vec<&str> = file_content.lines().collect();
     format!(
-        "part1: {}",
-        day03::manhattan_distance_from_cross_to_port(&day03::split_movements(&movements[0]), &day03::split_movements(&movements[1]))
+        "part1: {}, part2: {}",
+        day03::manhattan_distance_from_cross_to_port(&day03::split_movements(&movements[0]), &day03::split_movements(&movements[1])),
+        day03::first_cross_sum_of_lengths(&day03::split_movements(&movements[0]), &day03::split_movements(&movements[1]))
     )
 }
 
-- 
2.45.2