feat: rewrite 16 - power digit sum

.gitignore

@@ -1 +1,4 @@
 /target
+
+# only the first 100 solutions are allowed to be published
+src/bin/[1-9][0-9][0-9].rs

Cargo.lock

@@ -363,7 +363,6 @@ version = "1.0.0"
 dependencies = [
  "clap",
  "html-escape",
- "num-bigint",
  "num-to-words",
  "once_cell",
  "owo-colors",

Cargo.toml

@@ -15,7 +15,6 @@ html-escape = "0.2.13"
 phf = { version = "0.11.2", features = ["macros"] }
 rayon = "1.8.0"
 owo-colors = "3.5.0"
-num-bigint = "0.4.4"
 once_cell = "1.18.0"
 num-to-words = "0.1.1"
 

readme.md

@@ -5,14 +5,15 @@
 
 > My solutions to many of Project Euler's problems.
 
-All of the solutions here are written in rust. [main.rs](src/main.rs) is the home to my helper command line that can scaffold files for me quickly, prefaced with a statement of the problem! As per the rules of the challenge, I may only publish the solutions to the first 100 problems here, so I will stop after that but still continue the challenge.
+All of the solutions here are written in rust. [main.rs](src/main.rs) is the home to my helper command line that can scaffold files for me quickly, prefaced with a statement of the problem! As per the rules of the challenge, I may only publish the solutions to the first 100 problems here. I will continue the rest in my own time.
+
+Here is a [link to my profile](https://projecteuler.net/progress=newtykins).
 
 ### Allowed Dependencies
 
-- [rayon](https://lib.rs/rayon) for concurrency
-- [phf](https://lib.rs/phf) for compile-time static maps
+- [rayon](https://lib.rs/rayon) for concurrent iteration
+- [phf](https://lib.rs/phf) for compile-time hashmaps
 - [regex](https://lib.rs/regex) for regex (duh)
-- [num_bigint](https://lib.rs/num_bigint) for bigints
 
 ## Challenge Completion
 

src/bin/16.rs

@@ -5,36 +5,25 @@ Problem 16 - Power digit sum
 What is the sum of the digits of the number 2 1000 ?
 */
 
-use num_bigint::BigUint;
+fn power_digit_sum<const POWER: usize>(base: usize) -> usize {
+    let mut digits = [0u8; POWER];
+    digits[0] = 1; // 2^0 = 1
 
-fn get_digits(number: usize) -> Vec<u32> {
-    return number
-        .to_string()
-        .chars()
-        .map(|d| d.to_digit(10).unwrap())
-        .collect();
-}
+    for _ in 0..POWER {
+        let mut carry = 0;
 
-fn power_digit_sum(base: usize, power: u32) -> usize {
-    let answer = BigUint::new(get_digits(base))
-        .pow(power)
-        .to_string()
-        .chars()
-        .collect::<Vec<char>>();
-
-    let mut sum = 0;
-
-    for i in 0..answer.len() {
-        let number = answer[i].to_string().parse::<usize>().unwrap();
-
-        sum += number;
+        for digit in digits.iter_mut() {
+            let result = *digit as usize * base + carry;
+            *digit = result as u8 % 10;
+            carry = result / 10;
+        }
     }
 
-    sum
+    digits.iter().map(|&x| x as usize).sum()
 }
 
 pub fn main() {
-    let sum = power_digit_sum(2, 1000);
+    let sum = power_digit_sum::<1000>(2);
 
     println!("The sum of the digits of the number 2^1000 is {}!", sum);
 }

src/bin/19.rs

@@ -36,5 +36,5 @@ pub fn main() {
         }
     }
 
-    println!("The amount of Sundays that fell on the first of the month during the twentieth century is {}.", sundays_on_first);
+    println!("The amount of Sundays that fell on the first of the month during the twentieth century is {}!", sundays_on_first);
 }