Apparently a bug in PE 089 but can't for the life of me figure out what goes wrong

projecteuler/089/Cargo.lock

@@ -0,0 +1,32 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 3
+
+[[package]]
+name = "main"
+version = "0.1.0"
+dependencies = [
+ "nom",
+]
+
+[[package]]
+name = "memchr"
+version = "2.5.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "2dffe52ecf27772e601905b7522cb4ef790d2cc203488bbd0e2fe85fcb74566d"
+
+[[package]]
+name = "minimal-lexical"
+version = "0.2.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "68354c5c6bd36d73ff3feceb05efa59b6acb7626617f4962be322a825e61f79a"
+
+[[package]]
+name = "nom"
+version = "7.1.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d273983c5a657a70a3e8f2a01329822f3b8c8172b73826411a55751e404a0a4a"
+dependencies = [
+ "memchr",
+ "minimal-lexical",
+]

projecteuler/089/Cargo.toml

@@ -0,0 +1,9 @@
+[package]
+name = "main"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+nom = "7.1.3"

projecteuler/089/src/main.rs

@@ -0,0 +1,273 @@
+use nom::{
+    branch::alt,
+    character::complete::{char, multispace1},
+    multi::{many1, separated_list1},
+    IResult, Parser,
+};
+use std::{time::Instant, vec};
+
+#[derive(Debug, PartialEq, Eq, Clone, Copy)]
+enum RomanNum {
+    I,
+    V,
+    X,
+    L,
+    C,
+    D,
+    M,
+    Empty,
+}
+use RomanNum::*;
+type RomanNumeral = Vec<RomanNum>;
+
+// This function is not correct at all but I'm not gonna bother fixing it
+fn _is_minimal(number: &RomanNumeral) -> bool {
+    let mut last_num = Empty;
+    let mut occ = 0;
+
+    for num in number.iter() {
+        if *num == last_num {
+            occ += 1;
+        } else {
+            last_num = *num;
+            occ = 1;
+        }
+
+        if occ > 3 && (last_num == I || last_num == X || last_num == C) {
+            return false;
+            // } else if occ > 1 && (last_num == V || last_num == L || last_num == D) {
+            //     return false;
+        }
+    }
+
+    true
+}
+
+fn reduce(original: &RomanNumeral) -> RomanNumeral {
+    let mut last_num = Empty;
+    let mut occ = 0;
+    let mut result = vec![];
+
+    let mut number = original.clone();
+    number.push(Empty);
+
+    for num in number.iter() {
+        if *num == last_num {
+            occ += 1;
+
+            if occ == 10 {
+                match last_num {
+                    I => result.push(X),
+                    X => result.push(C),
+                    C => result.push(M),
+                    M => {
+                        for _ in 0..occ {
+                            result.push(M);
+                        }
+                    }
+                    _ => {}
+                }
+
+                occ -= 10;
+            }
+        } else {
+            if occ < 4 {
+                for _ in 0..occ {
+                    result.push(last_num);
+                }
+            } else if occ == 4 {
+                match last_num {
+                    I => {
+                        result.push(I);
+                        result.push(V);
+                    }
+                    X => {
+                        result.push(X);
+                        result.push(L);
+                    }
+                    C => {
+                        result.push(C);
+                        result.push(D);
+                    }
+                    M => {
+                        for _ in 0..occ {
+                            result.push(M);
+                        }
+                    }
+                    _ => {}
+                }
+            } else if occ == 5 {
+                match last_num {
+                    I => result.push(V),
+                    X => result.push(L),
+                    C => result.push(D),
+                    M => {
+                        for _ in 0..occ {
+                            result.push(M);
+                        }
+                    }
+                    _ => {}
+                }
+            } else if occ >= 6 && occ <= 8 {
+                match last_num {
+                    I => {
+                        result.push(V);
+                        for _ in 0..occ - 5 {
+                            result.push(I);
+                        }
+                    }
+                    X => {
+                        result.push(L);
+                        for _ in 0..occ - 5 {
+                            result.push(X);
+                        }
+                    }
+                    C => {
+                        result.push(D);
+                        for _ in 0..occ - 5 {
+                            result.push(C);
+                        }
+                    }
+                    M => {
+                        for _ in 0..occ {
+                            result.push(M);
+                        }
+                    }
+                    _ => {}
+                }
+            } else if occ == 9 {
+                match last_num {
+                    I => {
+                        result.push(I);
+                        result.push(X);
+                    }
+                    X => {
+                        result.push(X);
+                        result.push(C);
+                    }
+                    C => {
+                        result.push(C);
+                        result.push(M);
+                    }
+                    M => {
+                        for _ in 0..occ {
+                            result.push(M);
+                        }
+                    }
+                    _ => {}
+                }
+            }
+
+            last_num = *num;
+            occ = 1;
+        }
+        // println!("{:?}", result);
+    }
+
+    result
+}
+
+fn reduce_extra(numeral: &RomanNumeral) -> RomanNumeral {
+    if numeral.len() <= 3 {
+        return numeral.clone();
+    }
+
+    let mut result = vec![];
+    let mut window = vec![Empty, numeral[0], numeral[1]];
+    let mut i = 2;
+
+    while i < numeral.len() {
+        result.push(window[0]);
+        window[0] = window[1];
+        window[1] = window[2];
+        window[2] = numeral[i];
+
+        if window[0] == V && window[1] == I && window[2] == V {
+            result.push(I);
+            result.push(X);
+
+            window[1] = Empty;
+            window[2] = Empty;
+        } else if window[0] == L && window[1] == X && window[2] == L {
+            result.push(X);
+            result.push(C);
+
+            window[1] = Empty;
+            window[2] = Empty;
+        } else if window[0] == D && window[1] == C && window[2] == D {
+            result.push(C);
+            result.push(M);
+
+            window[1] = Empty;
+            window[2] = Empty;
+        }
+
+        i += 1;
+    }
+    result.push(window[0]);
+    result.push(window[1]);
+    result.push(window[2]);
+
+    result.into_iter().filter(|&n| n != Empty).collect()
+}
+
+fn parse_input(input: &str) -> IResult<&str, Vec<RomanNumeral>> {
+    let (input, result) = separated_list1(
+        multispace1,
+        many1(
+            alt((
+                char('I'),
+                char('V'),
+                char('X'),
+                char('L'),
+                char('C'),
+                char('D'),
+                char('M'),
+            ))
+            .map(|c| match c {
+                'I' => I,
+                'V' => V,
+                'X' => X,
+                'L' => L,
+                'C' => C,
+                'D' => D,
+                'M' => M,
+                _ => Empty,
+            }),
+        ),
+    )(input)?;
+
+    Ok((input, result))
+}
+
+fn main() {
+    println!("Hello, this is Patrick!");
+    let now = Instant::now();
+
+    let input_text = include_str!("../roman.txt");
+
+    // let res = parse_input(input_text);
+    // println!("{:?}", res);
+
+    let (_, numerals) = parse_input(input_text).unwrap();
+
+    let mut result = 0;
+    for mut numeral in numerals {
+        let start = numeral.len();
+        let mut s = start;
+        loop {
+            numeral = reduce(&numeral);
+            numeral = reduce_extra(&numeral);
+            if s == numeral.len() {
+                break;
+            }
+            s = numeral.len();
+        }
+        result += start - numeral.len();
+        println!("{:?} , {}", numeral, start - numeral.len());
+    }
+
+    println!("The number of characters that can be saved is: {}", result);
+
+    println!("Time passed: {:?}", Instant::now() - now);
+}