Day seven

day-07-rust/.gitignore

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+target/

day-07-rust/Cargo.lock

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+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 4
+
+[[package]]
+name = "day-07-rust"
+version = "0.1.0"

day-07-rust/Cargo.toml

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+[package]
+name = "day-07-rust"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]

day-07-rust/rust-toolchain.toml

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+[toolchain]
+channel = "nightly"

day-07-rust/src/common.rs

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+use std::io::{Bytes, Read};
+use std::iter::Peekable;
+
+pub type Number = i64;
+
+pub fn read_input_line<R: Read>(mut input: &mut Peekable<Bytes<R>>) -> Option<(Number, Vec<Number>)> {
+    let result = read_number(&mut input);
+    let mut parts = Vec::<Number>::with_capacity(20);
+    while let Some(Ok(ch)) = input.peek() {
+        match ch {
+            b'0'..=b'9' => parts.push(read_number(&mut input)),
+            b'\n' => {
+                input.next();
+                break
+            }
+            _ => {
+                input.next();
+            }
+        }
+    }
+    if parts.is_empty() {
+        None
+    } else {
+        Some((result, parts))
+    }
+}
+
+pub fn read_number<R: Read>(input: &mut Peekable<Bytes<R>>) -> Number {
+    let mut number: Number = 0;
+    while let Some(Ok(b'0'..=b'9')) = input.peek() {
+        number *= 10;
+        number += (input.next().unwrap().unwrap() - b'0') as Number;
+    }
+    number
+}

day-07-rust/src/main.rs

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+#![feature(let_chains)]
+
+mod task1;
+mod common;
+mod task2;
+
+fn main() {
+    let args = std::env::args().collect::<Vec<String>>();
+
+    if args.len() != 3 {
+        eprintln!("Usage: {} <1|2> <input file>", args[0]);
+        std::process::exit(1);
+    }
+
+    match args[1].as_str() {
+        "1" => task1::run(std::fs::File::open(&args[2]).expect("Failed to open input file")),
+        "2" => task2::run(std::fs::File::open(&args[2]).expect("Failed to open input file")),
+        _ => eprintln!("Unknown task: {}", args[1]),
+    }
+}

day-07-rust/src/task1.rs

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+use crate::common;
+use crate::common::Number;
+use std::io::{BufReader, Read};
+use std::ops::Rem;
+
+pub(crate) fn run<R: Read>(read: R) {
+    let mut reader = BufReader::new(read).bytes().peekable();
+
+    let mut total = 0;
+    while let Some((result, parts)) = common::read_input_line(&mut reader) {
+        if let Some(ops) = brute(result, &parts) {
+            println!("{:?} & {:?} => {}", ops, parts, result);
+            total += result;
+        }
+    }
+
+    println!("Result: {}", total);
+}
+
+fn brute(result: Number, parts: &[Number]) -> Option<Vec<char>> {
+    match parts.split_last() {
+        None => None,
+        Some((last, [])) => {
+            if result == *last {
+                Some(vec![])
+            } else {
+                None
+            }
+        }
+        Some((cur, parts)) => {
+            let test_result = result - cur;
+            if let Some(mut ops) = brute(test_result, parts) {
+                ops.push('+');
+                return Some(ops);
+            }
+            let test_result = result / cur;
+            if result.rem(cur) == 0 && let Some(mut ops) = brute(test_result, parts) {
+                ops.push('*');
+                return Some(ops);
+            }
+            None
+        }
+    }
+}

day-07-rust/src/task2.rs

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+use crate::common;
+use crate::common::Number;
+use std::io::{BufReader, Read};
+use std::ops::Rem;
+
+pub(crate) fn run<R: Read>(read: R) {
+    let mut reader = BufReader::new(read).bytes().peekable();
+
+    let mut total = 0;
+    while let Some((result, parts)) = common::read_input_line(&mut reader) {
+        if let Some(ops) = brute(result, &parts) {
+            println!("{:?} & {:?} => {}", ops, parts, result);
+            total += result;
+        }
+    }
+
+    println!("Result: {}", total);
+}
+
+fn brute(result: Number, parts: &[Number]) -> Option<Vec<char>> {
+    match parts.split_last() {
+        None => None,
+        Some((last, [])) => {
+            if result == *last {
+                Some(vec![])
+            } else {
+                None
+            }
+        }
+        Some((cur, parts)) => {
+            let test_result = result - cur;
+            if let Some(mut ops) = brute(test_result, parts) {
+                ops.push('+');
+                return Some(ops);
+            }
+            let test_result = result / cur;
+            if result.rem(cur) == 0 && let Some(mut ops) = brute(test_result, parts) {
+                ops.push('*');
+                return Some(ops);
+            }
+            let cur_str = cur.to_string();
+            let result_str = result.to_string();
+            if result_str.ends_with(cur_str.as_str()) {
+                let test_result = &result_str[..result_str.len() - cur_str.len()];
+                if !test_result.is_empty() && let Some(mut ops) = brute(test_result.parse().unwrap(), parts) {
+                    ops.push('|');
+                    return Some(ops);
+                }
+            }
+            None
+        }
+    }
+}