Add day04, 2019

2 files changed, 81 insertions, 0 deletions

diff --git a/2019/rust/day04/Cargo.toml b/2019/rust/day04/Cargo.toml
new file mode 100644
index 0000000..63acdbe
--- /dev/null
+++ b/2019/rust/day04/Cargo.toml
@@ -0,0 +1,8 @@
+[package]
+name = "day04"
+version = "0.1.0"
+authors = ["cos <cos>"]
+edition = "2018"
+
+[dependencies]
+itertools = "*"
diff --git a/2019/rust/day04/src/main.rs b/2019/rust/day04/src/main.rs
new file mode 100644
index 0000000..c4cadef
--- /dev/null
+++ b/2019/rust/day04/src/main.rs
@@ -0,0 +1,73 @@
+use itertools::Itertools;
+use std::env;
+
+fn is_increasing(n:u32) -> bool {
+    for (l, r) in (0..5).rev().map(|e| n/10u32.pow(e)%10)
+        .zip((1..6).rev().map(|e| n/10u32.pow(e)%10))
+    {
+        if l < r { return false; }
+    }
+
+    true
+}
+
+fn has_repeated(n:u32) -> bool {
+    for (l, r) in (0..5).rev().map(|e| n/10u32.pow(e)%10)
+        .zip((1..6).rev().map(|e| n/10u32.pow(e)%10))
+    {
+        if l == r { return true; }
+    }
+
+    false
+}
+fn has_double(n:u32) -> bool {
+    #[derive(Debug, PartialEq)]
+    enum State { NoMatch, Matching, TooLong, Verified };
+    let mut state = State::NoMatch;
+
+    for (l, r) in (0..5).rev().map(|e| n/10u32.pow(e)%10)
+        .zip((1..6).rev().map(|e| n/10u32.pow(e)%10))
+    {
+        state = match state {
+            State::NoMatch  => if l == r { State::Matching } else { State::NoMatch },
+            State::Matching => if l == r { State::TooLong  } else { State::Verified },
+            State::TooLong  => if l == r { State::TooLong  } else { State::NoMatch },
+            State::Verified => State::Verified,
+        };
+        if state == State::Verified { break; }
+    }
+
+    state == State::Verified || state == State::Matching
+}
+
+fn first_puzzle(input:String) -> usize {
+    let ( start, end ) = input.split("-")
+        .map(|s| s.parse::<u32>().unwrap())
+        .next_tuple().unwrap();
+
+    (start..=end)
+        .filter(|n| is_increasing(*n))
+        .filter(|n| has_repeated(*n))
+        .count()
+}
+
+fn second_puzzle(input:String) -> usize {
+    let ( start, end ) = input.split("-")
+        .map(|s| s.parse::<u32>().unwrap())
+        .next_tuple().unwrap();
+
+    (start..=end)
+        .filter(|n| is_increasing(*n))
+        .filter(|n| has_double(*n))
+        .count()
+}
+
+fn main() {
+    let input = env::args().nth(1).expect("Please provide a valid range as first argument.");
+
+    let first = first_puzzle(input.clone());
+    println!("Solution to first part: {}.", first);
+
+    let second = second_puzzle(input);
+    println!("Solution to second part: {}.", second);
+}