From adaa608e31f0a5b75055fc9fb27081d6c88ba055 Mon Sep 17 00:00:00 2001
From: newt <hi@newty.dev>
Date: Wed, 9 Oct 2024 18:10:12 +0100
Subject: [PATCH] feat: 19 - counting sundays

---
 readme.md           |  4 ++--
 src/bin/19.rs       | 40 ++++++++++++++++++++++++++++++++++++++++
 src/commands/run.rs |  3 +++
 src/problem.rs      | 16 ++++++++--------
 4 files changed, 53 insertions(+), 10 deletions(-)
 create mode 100644 src/bin/19.rs

diff --git a/readme.md b/readme.md
index 2c82865..8874073 100644
--- a/readme.md
+++ b/readme.md
@@ -16,7 +16,7 @@ All of the solutions here are written in rust. [main.rs](src/main.rs) is the hom
 
 ## Challenge Completion
 
-### 22 out of 100 public challenges completed.
+### 23 out of 100 public challenges completed.
 
 - [x] 1 - [Multiples of 3 or 5](src/bin/1.rs)
 - [x] 2 - [Even Fibonacci numbers](src/bin/2.rs)
@@ -36,7 +36,7 @@ All of the solutions here are written in rust. [main.rs](src/main.rs) is the hom
 - [x] 16 - [Power digit sum](src/bin/16.rs)
 - [x] 17 - [Number letter counts](src/bin/17.rs)
 - [x] 18 - [Maximum path sum I](src/bin/18.rs)
-- [ ] 19 - Counting Sundays
+- [x] 19 - Counting Sundays
 - [ ] 20 - Factorial digit sum
 - [ ] 21 - Amicable numbers
 - [x] 22 - [Names scores](src/bin/22.rs)
diff --git a/src/bin/19.rs b/src/bin/19.rs
new file mode 100644
index 0000000..099f681
--- /dev/null
+++ b/src/bin/19.rs
@@ -0,0 +1,40 @@
+/*
+Problem 19 - Counting Sundays
+
+You are given the following information, but you may prefer to do some research for yourself.
+1 Jan 1900 was a Monday.
+Thirty days has September,
+April, June and November.
+All the rest have thirty-one,
+Saving February alone,
+Which has twenty-eight, rain or shine.
+And on leap years, twenty-nine.
+A leap year occurs on any year evenly divisible by 4, but not on a century unless it is divisible by 400.
+How many Sundays fell on the first of the month during the twentieth century (1 Jan 1901 to 31 Dec 2000)?
+*/
+fn is_leap_year(year: u16) -> bool {
+    (year % 4 == 0 && year % 100 != 0) || year % 400 == 0
+}
+
+pub fn main() {
+    let mut sundays_on_first = 0;
+    let days_in_month = [31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31];
+    let mut current_day = 1; // January 1, 1901 was a Tuesday, so starting with 1 (Tuesday)
+
+    for year in 1901..=2000 {
+        for (month, &days) in days_in_month.iter().enumerate() {
+            if month == 1 && is_leap_year(year) {
+                current_day = (current_day + 29) % 7; // Leap year
+            } else {
+                current_day = (current_day + days) % 7; // Regular year
+            }
+
+            if current_day == 0 {
+                // Checking if the first day of the month is a Sunday (6 represents Sunday)
+                sundays_on_first += 1;
+            }
+        }
+    }
+
+    println!("The amount of Sundays that fell on the first of the month during the twentieth century is {}.", sundays_on_first);
+}
diff --git a/src/commands/run.rs b/src/commands/run.rs
index ef896ae..faf8dc9 100644
--- a/src/commands/run.rs
+++ b/src/commands/run.rs
@@ -20,6 +20,8 @@ mod four;
 mod fourteen;
 #[path = "../bin/9.rs"]
 mod nine;
+#[path = "../bin/19.rs"]
+mod nineteen;
 #[path = "../bin/1.rs"]
 mod one;
 #[path = "../bin/7.rs"]
@@ -84,6 +86,7 @@ pub async fn execute(
         22 => twenty_two::main(),
         27 => twenty_seven::main(),
         67 => sixty_seven::main(),
+        19 => nineteen::main(),
         _ => {
             exists = false;
             println!(
diff --git a/src/problem.rs b/src/problem.rs
index 0d8dfc3..af10ee0 100644
--- a/src/problem.rs
+++ b/src/problem.rs
@@ -64,7 +64,7 @@ impl Problem {
         let number = number
             .unwrap_or_else(|| Self::prompt_number("Please select a problem:", false).unwrap());
 
-        let body = reqwest::get(format!("https://projecteuler.net/problem={number}"))
+        let body = reqwest::get(format!("https://projecteuler.net/minimal={number}"))
             .await?
             .text()
             .await?;
@@ -105,14 +105,14 @@ impl Problem {
     pub fn file_body(&self) -> String {
         format!(
             "/*
-    Problem {} - {}
+Problem {} - {}
+
+{}
+*/
     
-    {}
-    */
-    
-    pub fn main() {{
-        println!(\"Hello World!\");
-    }}",
+pub fn main() {{
+    println!(\"Hello World!\");
+}}",
             self.number,
             html_escape::decode_html_entities(&self.title).to_string(),
             html_escape::decode_html_entities(&self.content)