feat(24): complete lexicographic permutations

readme.md

@@ -17,7 +17,7 @@ Here is a [link to my profile](https://projecteuler.net/progress=newtykins).
 
 ## Challenge Completion
 
-### 26 out of 100 public challenges completed.
+### 27 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)
@@ -42,7 +42,7 @@ Here is a [link to my profile](https://projecteuler.net/progress=newtykins).
 - [x] 21 - Amicable numbers
 - [x] 22 - [Names scores](src/bin/22.rs)
 - [x] 23 - Non-abundant sums
-- [ ] 24 - Lexicographic permutations
+- [x] 24 - Lexicographic permutations
 - [ ] 25 - 1000-digit Fibonacci number
 - [ ] 26 - Reciprocal cycles
 - [x] 27 - [Quadratic primes](src/bin/27.rs)

src/bin/24.rs

@@ -0,0 +1,54 @@
+/*
+Problem 24 - Lexicographic Permutations
+
+A permutation is an ordered arrangement of objects. For example, 3124 is one possible permutation of the digits 1, 2, 3 and 4. If all of the permutations are listed numerically or alphabetically, we call it lexicographic order. The lexicographic permutations of 0, 1 and 2 are:
+012   021   102   120   201   210
+What is the millionth lexicographic permutation of the digits 0, 1, 2, 3, 4, 5, 6, 7, 8 and 9?
+*/
+
+fn permutations<T>(array: Vec<T>) -> Vec<Vec<T>>
+where
+    T: Clone,
+{
+    let mut out = vec![];
+
+    match array.len() {
+        0 => vec![],
+        1 => vec![array],
+        _ => {
+            for i in 0..array.len() {
+                let mut array = array.clone();
+                let first = array.remove(i);
+                let mut permutations = permutations(array);
+
+                for permutation in permutations.iter_mut() {
+                    permutation.insert(0, first.clone());
+                }
+
+                out.append(&mut permutations);
+            }
+
+            out
+        }
+    }
+}
+
+fn nth_lexicographic_permutation(array: Vec<usize>, n: usize) -> Vec<usize> {
+    let mut permutations = permutations(array);
+    permutations.sort();
+
+    permutations[n - 1].clone()
+}
+
+pub fn main() {
+    let digits = (0..10).collect::<Vec<usize>>();
+    let millionth_permutation = nth_lexicographic_permutation(digits, 1_000_000);
+
+    println!(
+        "The millionth lexicographic permutation of the digits 0-9 is {}!",
+        millionth_permutation
+            .iter()
+            .map(|&d| d.to_string())
+            .collect::<String>()
+    );
+}

src/commands/run.rs

@@ -54,6 +54,8 @@ mod twenty_three;
 mod twenty_two;
 #[path = "../bin/2.rs"]
 mod two;
+#[path = "../bin/24.rs"]
+mod twenty_four;
 
 pub async fn execute(
     problem: Option<u8>,
@@ -96,6 +98,7 @@ pub async fn execute(
         20 => twenty::main(),
         21 => twenty_one::main(),
         23 => twenty_three::main(),
+        24 => twenty_four::main(),
         _ => {
             exists = false;
             println!(
@@ -119,4 +122,4 @@ Time elapsed when executing problem {} is: {:?}",
     }
 
     Ok(())
-}
+}

src/main.rs

@@ -30,9 +30,11 @@ struct RunArgs {
 #[derive(Subcommand)]
 enum Commands {
     /// Handles the initialisation of a new Project Euler Problem
+    #[clap(alias = "n")]
     New(NewArgs),
 
     /// Runs the solution to a problem
+    #[clap(alias = "r")]
     Run(RunArgs),
 }