Advent 2023 Day 3

advent_of_code_2023/day3/main2.rs

@@ -0,0 +1,73 @@
+use std::cmp::min;
+use std::collections::HashMap;
+use std::fs::read_to_string;
+
+fn register_gears(schematic: &Vec<Vec<char>>, gear_mapping: &mut HashMap<(usize, usize), Vec<usize>>, number: usize, line: usize, start: usize, end: usize) {
+    let first_line = if line != 0 { line - 1 } else { line };
+    let last_line = min(schematic.len() - 1, line + 1);
+    let first_char = if start != 0 { start - 1 } else { start };
+    let last_char = min(schematic[line].len() - 1, end);
+    
+    for line_idx in first_line..=last_line {
+        for char_idx in first_char..=last_char {
+            if schematic[line_idx][char_idx] == '*' {
+                gear_mapping.entry((line_idx, char_idx)).or_insert(Vec::new()).push(number);
+            }
+        }
+    }
+}
+
+fn parse_number(line: &Vec<char>, mut caret: usize) -> (Option<i32>, usize) {
+    if !line[caret].is_ascii_digit() {
+        return (None, caret + 1);
+    }
+
+    let start = caret;
+    let end = loop {
+        caret += 1;
+        if caret == line.len() || !line[caret].is_ascii_digit() {
+            break caret;
+        }
+    };
+
+    (Some(line[start..end].iter().collect::<String>().parse::<i32>().unwrap()), caret)
+}
+
+fn main() {
+    let schematic: Vec<Vec<char>> = read_to_string("input.txt").unwrap().lines().map(|line| {
+        line.chars().collect()
+    }).collect();
+
+    let mut gear_mapping: HashMap<(usize, usize), Vec<usize>> = HashMap::new();
+
+    let mut line = 0;
+    while line < schematic.len() {
+        let mut caret = 0;
+
+        while caret < schematic[line].len() {
+            let (number, next) = parse_number(&schematic[line], caret);
+
+            match number {
+                Some(_) => (),
+                None => {
+                    caret = next;
+                    continue;
+                }
+            }
+
+            register_gears(&schematic, &mut gear_mapping, number.unwrap() as usize, line, caret, next);
+            caret = next;
+        }
+
+        line += 1;
+    }
+
+    let mut sum = 0;
+    for gear in gear_mapping.values() {
+        if gear.len() == 2 {
+            sum += gear[0] * gear[1];
+        }
+    }
+
+    println!("sum: {}", sum);
+}