diff --git a/day-03/Cargo.toml b/day-03/Cargo.toml
new file mode 100644
index 0000000..51cc795
--- /dev/null
+++ b/day-03/Cargo.toml
@@ -0,0 +1,8 @@
+[package]
+name = "day-03"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
diff --git a/day-03/input.txt b/day-03/input.txt
new file mode 100644
index 0000000..c5ec2fc
--- /dev/null
+++ b/day-03/input.txt
@@ -0,0 +1,140 @@
+.854...........................................................................362...........271...732........838.........24................
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+...........749*...-...+..330.....................215%...*................725.....953........%.................*............639......331.419.
+.......706.....59.............*....=...262.............678...........857.*............189....................912.+589.846*...*..............
+..........*................393.59..418....*................151...........594...........*....584*258.......................17.997............
+.......774....275........................777........841..............988.........121....908.........86.....482..295....................@....
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+...................................287.$......930.....&.....*528.........332............755..................840../.............583.....209.
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+....*........-902..2.123..*...912.......775......./...............241........734....90.968.513..66.566...................*..&...............
+..................*....@.923...*.......*.....289..47.....785..710.......54................*......*....................767....452....=....597
+.............348.362............607.....889.....#........*....*........*......$904................694...............................241.....
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+.908$...*...........&..861...........=.....%....240............-..+..9.514...615.....&....-646.....538...144.751...........899.........545..
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+.......%...........379..377.....770@.................$.....126....*...712.287....951.........*......984*..........+.............+700........
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+..559..........................393.........766...789.............683..................461..#......910.........904.........$.%......*.....13.
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+.....923.285*.....961...........*......$812......812..851.............678.29.......*......501.....228..............385...853...........251..
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+......$....250=.....965...*.............................113...$......766....$.......941........-......658.............894........351........
+......335...............463.328*.....411....%.............................981.113......*5.............*...773=.573&....*............$.......
+..........%348..................460.....*5..517.......583.261.....889@.......................953.....496...............547............620...
+...299.................367.......................+....*................852.442.796.........*.@...............=................834.....*.....
+....*....772...487.......................#......938.462.956..41.643...*.....#.....*592....66...809.368..3..549........................772...
+.566........*.....*320.....498..775.230.193....................*......961.........................*....*.......%283.....406.......495.......
+........292..585..............*.*.....*..........213...*309...................469..549......413........903................*....29..*........
+.........*.......@.........551..806...489......................51.655.999*.......*.$.............21*.................300..931....*..595.....
+......878......62../...........................871......169..=..&..*......235..788...497..........................68....*.......191.........
+.144.........+.....31............-...............*..623*....428.....955...............*.............424....89....*......728.............*665
+.............447...............530...203...955.336..........................227........665.......$.........*.....669..............473.......
+835...................*323..............*./...........=.....24..........*.........................452.......9.............263.........570...
+......568...803@.....................152.......209.933.....*....877..667.895............548...963......................................*....
+.......$.........=............................*...........948..-...................171.*........*.605.765..-........90..............992.....
+..360..........#.476...........................564../.............755*...............+..709...11.....*......909..........696..124%..........
+........74...73................320.........658......739...=...........484...860*....................................314.....................
+...=509...*.........79.290........*...222...*.............46...940..............960.....473.....320..........$681......*591..269....../.....
+........887.94@......*..*.........302...+.784.554+............+......#......455........./............891..........457........*...609.120....
+....................874.246.....................................+.....228..*....&.........272....%..$.....*377.....*..52..604....%..........
+.....44.....870*457................905.45......58...............956.........935.551...807..$.....21....356.......317....................%...
+.........=...................267......*...300=.........543..............398..............#.................$.......................386...745
+..........145......+............................*......*...........7....$.............64...........646....675..1..930..770.....791.$........
+................744....462......443&......*389..575..965...805....+..14.......761*578..-...#..776...*..................-........-.......822.
+....668.484...............*............875.................*.........*....................227...*..908.............215......*.......270.....
+.......*......771..........318....883......881...........655.@26..130..799.......876..91......28...........699.........807...510............
+.............-........391*.........*.......+......903..................*.....379.*....@...........713........#............*.................
+..........+................196..230...........411....*965..682.......873....$.....916....755....&..=.....................296......+958.983..
+...*.....718.......279........%...............................*.271.............@.......*......932.......621..637.843..................*....
+..59..........%2...........................................400...*...142.870...746......256..........865*...........%...=.....%...409...761.
+............@...........122*157...........394........%.444.....207...-......*.........................................434..827...*..........
+.....266..19.....=..............624.......*........398....*................373...........418...16.....654.878*.................890..........
+...............487..........884....*......199.227........723......914*411...........228..........%...................872................-...
+.....937..608.................*....306........$....................................*..................522..309.@16.....*.............765....
+......#....................128../.................%136....140.................773...114...........33....*....*.........615.....303..........
+.249.....590..$...949..768.......380......%...996..............833...28...310.#...................*..338.....770...559......................
+...+.854.../.678..*....................646...*.........................=...&..............#.....422...................#.231...714.122.......
+......*...........552........................741..........+.......437........455*768..134..69..........*........519.......*........*........
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+......................%.....288...............*...-.......617...........-..677........*.....32..........-907.+........*.....=....48.475.....
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+........*.......%...........596....=.*....................863................$................428..*......899.....................114.......
+.595=.112.737.699................382.888..........................315...@...325..........480........115..*.........-......368...............
+...........*......+.@......652.*...............................&.....@..182.......219$.........945+.............844...........996....744*...
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+...+........................$........+..967*.........*....921......321......%................612@....*......................44..............
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+..........................................*..392..&.........505...957.@.........158...285......881#....497.........+...*....................
+.........=../..../.....588........227....639............741*..........443..681..........+..153........................335...................
+........201.671.96......$............*.....................................*........415.......*........-.......155...........848.58&........
+............................922......92...........180..........................&39...%....208..389......696.....*............=.......883.852
+....237.........950.........*............80..............................................*....................657.......................*...
+....../..611.......*.....671...443...971.&....366....381...442....458...$.......589.343.397.....463.......60.......&........125......&......
+..853...../..945..564...........*......*.......@......-................783..........*.......................*.......28......=.........373...
+................*.......+843..550..998.973.........+.....208.565..@..............231......292............+.365..172............+............
+......117......615..................*............299............&..862.895............/86...*....114..552........*...697.....733...388......
+.....................................212..261........885...............*...903..26*..........50.....-..........158................*.........
+...../........11..360....748......................67....*272.....320...16.....*....137.905......239......470......................433.......
+...141........*.....%......+......967........-...%...........243...*.......904............*....*..............88.377......619...............
+................=.....-668....%.....=.+461..525.....662.....*......196..28..............778...940..400..682...*...*.........*..638*.........
+779#..113........209...........744....................*...144..811....../...#......................-...*.....297..713.....50................
+.........$................#.........844...6...........62.......*.............957...&.......112@.......211.............173....989............
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+...*..290...573......*............437....227.....53......132............#....471%.............501..%..................733.....270.....=.....
+..637...*............596............................=....*.......400...............*...........*....................................#.......
+......958.....757%.........=.........228......624...746.81../.....*........../..718.198..38...184..............*820..774......./830.693.....
+.........................453...405.=...=....................100.144.......728...........*...................498............$................
+..616............................*.756...310.........#52.............130.......=........506.....509.779..........723.......182..+...........
+...*....49.....-..............551..........*................789./.....*......306...613........./......*..491....*...............791..931....
+...863.....%.72......832.653........*490....814.....984.....=...741...568..........*.................998........567........+........#.......
+.........171..........*..-.......406...............*....389.....................486.....630............../...............457.576............
+..............308..515..................373@......709..&..............*185..................689..........751........44..........*764........
+..............*..............661....=.........*.............993....984.....*.......908......=...273............../.*........................
+.......582..335...260....59......998../.....39.760.313*174...*..........@.183......................*47....&994.887.577........*464.....22...
+......*...............................449..................802........762.....522..139+..154..266$......................46.323.....712*.....
+....827.....................................35......600*29.....724........488............*...............149*227.........*..................
+........@......278*............@..135..........594.........470*...........*....540*.......42..............................775.536..790......
+.....990...........742......181....*..............*..@521................743.......552............310...*....+738.....................*.....
+.......................125.......311............715........263...........................................173...................235....291...
\ No newline at end of file
diff --git a/day-03/src/main.rs b/day-03/src/main.rs
new file mode 100644
index 0000000..0c4f80a
--- /dev/null
+++ b/day-03/src/main.rs
@@ -0,0 +1,169 @@
+use std::collections::BTreeMap;
+
+#[derive(Debug, Clone)]
+enum Value {
+    Digit(u32),
+    Symbol(char),
+}
+
+#[derive(Debug, Clone, Default, PartialOrd, Ord, Eq, PartialEq)]
+struct Address {
+    row: i32,
+    col: i32,
+}
+
+fn part_1(input: &str) -> u32 {
+    let numbers = input
+        .lines()
+        .enumerate()
+        .flat_map(|(row, line)| {
+            extract_numbers(line)
+                .into_iter()
+                .map(move |(col, len, number)| {
+                    (
+                        (col..col + len)
+                            .map(|c| Address {
+                                row: row as i32,
+                                col: c as i32,
+                            })
+                            .collect::<Vec<_>>(),
+                        number,
+                    )
+                })
+        })
+        .collect::<Vec<(Vec<Address>, u32)>>();
+
+    let grid = input
+        .lines()
+        .enumerate()
+        .flat_map(|(row, line)| {
+            line.chars().enumerate().map(move |(col, character)| {
+                (
+                    Address {
+                        row: row as i32,
+                        col: col as i32,
+                    },
+                    match character {
+                        '.' => None,
+                        c if c.is_ascii_digit() => Some(Value::Digit(c.to_digit(10).unwrap())),
+                        c => Some(Value::Symbol(c)),
+                    },
+                )
+            })
+        })
+        .collect::<BTreeMap<Address, Option<Value>>>();
+
+    let symbols: BTreeMap<Address, char> = grid
+        .iter()
+        .filter_map(|(address, value)| match value {
+            Some(Value::Symbol(c)) => Some((address.clone(), *c)),
+            _ => None,
+        })
+        .collect();
+
+    let mut sum = 0;
+    for (addresses, number) in numbers {
+        if addresses
+            .iter()
+            .flat_map(bounding_box)
+            .any(|a| symbols.contains_key(&a))
+        {
+            sum += number;
+        }
+    }
+
+    sum
+}
+
+fn extract_numbers(input: &str) -> Vec<(usize, usize, u32)> {
+    let mut result = Vec::default();
+    let mut current_number = String::new();
+    let mut current_offset = 0;
+
+    for (offset, c) in input.chars().enumerate() {
+        if c.is_ascii_digit() {
+            current_number.push(c);
+            current_offset = offset + 1;
+        } else if !current_number.is_empty() {
+            result.push((
+                current_offset - current_number.len(),
+                current_number.len(),
+                current_number.parse::<u32>().unwrap(),
+            ));
+            current_number.clear();
+        }
+    }
+
+    if !current_number.is_empty() {
+        result.push((
+            current_offset - current_number.len(),
+            current_number.len(),
+            current_number.parse::<u32>().unwrap(),
+        ));
+    }
+
+    result
+}
+
+fn bounding_box(address: &Address) -> Vec<Address> {
+    vec![
+        Address {
+            row: address.row - 1,
+            col: address.col - 1,
+        },
+        Address {
+            row: address.row - 1,
+            col: address.col,
+        },
+        Address {
+            row: address.row - 1,
+            col: address.col + 1,
+        },
+        Address {
+            row: address.row,
+            col: address.col - 1,
+        },
+        Address {
+            row: address.row,
+            col: address.col + 1,
+        },
+        Address {
+            row: address.row + 1,
+            col: address.col - 1,
+        },
+        Address {
+            row: address.row + 1,
+            col: address.col,
+        },
+        Address {
+            row: address.row + 1,
+            col: address.col + 1,
+        },
+    ]
+}
+
+fn main() {
+    let input = include_str!("../input.txt");
+    println!("Part 1: {}", part_1(input));
+}
+
+#[cfg(test)]
+mod test {
+    use std::vec;
+
+    use super::*;
+
+    #[test]
+    fn test_extract_number() {
+        assert_eq!(
+            extract_numbers("123..45.6"),
+            vec![(0, 3, 123), (5, 2, 45), (8, 1, 6)]
+        );
+    }
+
+    #[test]
+    fn test_part1() {
+        let input = include_str!("../test-input.txt");
+        assert_eq!(part_1(input), 4361);
+    }
+}
diff --git a/day-03/test-input.txt b/day-03/test-input.txt
new file mode 100644
index 0000000..624ea4f
--- /dev/null
+++ b/day-03/test-input.txt
@@ -0,0 +1,10 @@
+467..114..
+...*......
+..35..633.
+......#...
+617*......
+.....+.58.
+..592.....
+......755.
+...$.*....
+.664.598..
\ No newline at end of file