From 2c64ab4657f61cd4b7b597a4cd698ae41818a6c3 Mon Sep 17 00:00:00 2001
From: newt <hi@newty.dev>
Date: Wed, 9 Oct 2024 18:10:11 +0100
Subject: [PATCH] feat: 16 - power digit sum

depends on num_bigint::BigUint
---
 Cargo.lock    | 31 +++++++++++++++++++++++++++++++
 Cargo.toml    |  1 +
 readme.md     |  4 ++--
 src/bin/16.rs | 35 +++++++++++++++++++++++++++++++++++
 4 files changed, 69 insertions(+), 2 deletions(-)
 create mode 100644 src/bin/16.rs

diff --git a/Cargo.lock b/Cargo.lock
index be3411c..b683006 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -251,6 +251,7 @@ version = "1.0.0"
 dependencies = [
  "clap",
  "html-escape",
+ "num-bigint",
  "owo-colors",
  "regex",
  "requestty",
@@ -719,6 +720,36 @@ version = "0.1.14"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "72ef4a56884ca558e5ddb05a1d1e7e1bfd9a68d9ed024c21704cc98872dae1bb"
 
+[[package]]
+name = "num-bigint"
+version = "0.4.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f93ab6289c7b344a8a9f60f88d80aa20032336fe78da341afc91c8a2341fc75f"
+dependencies = [
+ "autocfg",
+ "num-integer",
+ "num-traits",
+]
+
+[[package]]
+name = "num-integer"
+version = "0.1.45"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "225d3389fb3509a24c93f5c29eb6bde2586b98d9f016636dff58d7c6f7569cd9"
+dependencies = [
+ "autocfg",
+ "num-traits",
+]
+
+[[package]]
+name = "num-traits"
+version = "0.2.15"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "578ede34cf02f8924ab9447f50c28075b4d3e5b269972345e7e0372b38c6cdcd"
+dependencies = [
+ "autocfg",
+]
+
 [[package]]
 name = "num_cpus"
 version = "1.15.0"
diff --git a/Cargo.toml b/Cargo.toml
index c2f1f49..eb902f3 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -13,6 +13,7 @@ reqwest = "0.11"
 tokio = { version = "1.23", features = ["full"] }
 regex = "1"
 html-escape = "0.2.13"
+num-bigint = "0.4.3"
 
 [profile.release]
 opt-level = "z"
diff --git a/readme.md b/readme.md
index 137e426..c908a11 100644
--- a/readme.md
+++ b/readme.md
@@ -11,7 +11,7 @@ I originally started the challenge in [the-honk](https://github.com/newtykins/th
 
 ## Challenge Completion
 
-### <!-- completed -->19<!-- completed --> out of 100 public challenges completed.
+### <!-- completed -->20<!-- completed --> 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)
@@ -28,7 +28,7 @@ I originally started the challenge in [the-honk](https://github.com/newtykins/th
 - [x] 13 - [Large sum](src/bin/13.rs)
 - [x] 14 - [Longest Collatz sequence](src/bin/14.rs)
 - [x] 15 - [Lattice paths](src/bin/15.rs)
-- [ ] 16 - Power digit sum
+- [x] 16 - [Power digit sum](src/bin/16.rs)
 - [ ] 17 - Number letter counts
 - [ ] 18 - Maximum path sum I
 - [ ] 19 - Counting Sundays
diff --git a/src/bin/16.rs b/src/bin/16.rs
new file mode 100644
index 0000000..3896ac4
--- /dev/null
+++ b/src/bin/16.rs
@@ -0,0 +1,35 @@
+/*
+Problem 16 - Power digit sum
+
+2 15  = 32768 and the sum of its digits is 3 + 2 + 7 + 6 + 8 = 26.
+What is the sum of the digits of the number 2 1000 ?
+*/
+use num_bigint::BigUint;
+
+fn get_digits(number: usize) -> Vec<u32> {
+    return number
+        .to_string()
+        .chars()
+        .map(|d| d.to_digit(10).unwrap())
+        .collect();
+}
+
+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;
+    }
+
+    sum
+}
+
+fn main() {
+    let sum = power_digit_sum(2, 1000);
+
+    println!("The sum of the digits of the number 2^1000 is {}!", sum);
+}