diff --git a/Cargo.toml b/Cargo.toml
index 1438192..b85788e 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -70,3 +70,7 @@ path = "src/day16.rs"
 [[bin]]
 name = "day17"
 path = "src/day17.rs"
+
+[[bin]]
+name = "day18"
+path = "src/day18.rs"
diff --git a/inputs/day18.txt b/inputs/day18.txt
new file mode 100644
index 0000000..9b65fac
--- /dev/null
+++ b/inputs/day18.txt
@@ -0,0 +1,100 @@
+[[[[7,1],[0,0]],[6,[8,2]]],[8,[3,8]]]
+[[[3,6],[9,4]],[[[5,9],5],[8,0]]]
+[[[2,2],2],[1,[[1,6],7]]]
+[[[[0,9],7],[[3,2],8]],[6,[7,9]]]
+[[[[4,1],6],[[7,6],[2,2]]],[[[1,1],9],4]]
+[[[8,[3,7]],3],[[4,4],[[9,1],[3,5]]]]
+[[4,[8,2]],[1,[0,5]]]
+[8,[8,7]]
+[[[[2,2],7],[3,[4,5]]],[[4,6],[[2,5],4]]]
+[[[5,5],[[5,1],3]],[[2,[8,2]],[[6,9],[1,5]]]]
+[0,7]
+[[[[5,1],3],[8,[5,3]]],7]
+[[5,[2,[0,6]]],[[[5,5],2],[9,[8,0]]]]
+[[[[3,4],2],0],4]
+[[[[5,3],[2,7]],6],[[4,0],[9,[7,2]]]]
+[[[3,[2,5]],[3,3]],7]
+[[[[5,1],1],[4,8]],[[5,[8,3]],2]]
+[[4,[[8,1],[8,5]]],[[[4,1],0],6]]
+[[[5,5],[5,9]],[0,[[6,8],[0,1]]]]
+[4,[[[7,9],4],0]]
+[[[[0,1],7],[[3,6],5]],[8,[5,[6,1]]]]
+[[[7,7],[8,0]],[6,[8,[7,9]]]]
+[[[9,2],1],6]
+[[[4,4],[2,[5,0]]],[[[2,6],6],[5,[4,3]]]]
+[[2,[[4,7],5]],1]
+[[8,7],[[[2,0],7],[1,[0,3]]]]
+[[9,[[9,3],[9,5]]],[[8,7],[[4,1],[6,5]]]]
+[[3,4],[[9,4],5]]
+[[5,[[8,3],5]],1]
+[[0,[[9,0],[3,2]]],[2,[7,[5,1]]]]
+[[9,[[9,5],[8,6]]],[[4,4],[[3,8],[1,6]]]]
+[[[1,[5,2]],9],[[4,6],[3,[8,0]]]]
+[[1,7],[[1,7],9]]
+[[[[3,4],3],[[7,5],[9,1]]],[[[5,0],[3,0]],[[7,9],6]]]
+[[[7,2],[[1,0],[5,6]]],[[[3,7],[8,9]],6]]
+[[[[1,1],1],[[8,6],[9,8]]],[[[1,8],4],[8,9]]]
+[[[8,9],0],3]
+[[[1,7],[1,[3,9]]],[6,[0,[8,5]]]]
+[[0,5],[6,5]]
+[[[[6,8],[4,5]],[[7,4],6]],[[3,6],5]]
+[[8,[[0,9],8]],[9,[7,[7,9]]]]
+[0,[[[7,1],2],[[0,4],4]]]
+[[0,[[9,1],5]],[1,4]]
+[3,4]
+[[[9,3],[1,3]],[[[4,8],3],[[1,3],[9,0]]]]
+[[[[5,1],7],[[9,2],8]],[[[6,8],[5,4]],[0,1]]]
+[8,[[1,[3,0]],[[7,9],4]]]
+[[[6,4],[[2,9],[9,0]]],[7,[[0,0],3]]]
+[[3,[[9,6],6]],2]
+[[5,[[3,1],[7,5]]],[[[6,7],9],[[4,6],[5,2]]]]
+[[[4,[6,5]],8],[[6,[8,0]],[[9,3],3]]]
+[[[[4,9],[2,8]],9],[[[5,0],0],[[3,4],[2,8]]]]
+[[3,[7,1]],[9,[[1,8],7]]]
+[[9,1],[0,[[0,7],[7,1]]]]
+[[7,[0,[7,6]]],[[[5,3],1],[6,[4,5]]]]
+[8,[[[2,1],[6,9]],[[3,3],[4,6]]]]
+[0,[7,[3,0]]]
+[[[[1,6],3],[5,[8,0]]],[[[6,6],7],1]]
+[[[7,[8,3]],3],[[[2,8],5],[0,[9,5]]]]
+[[[[5,1],4],[[1,2],1]],7]
+[[[3,[7,5]],7],3]
+[[9,[6,[1,1]]],[[[4,1],[2,2]],[[9,5],[7,7]]]]
+[2,7]
+[[[9,[8,6]],[[9,0],[6,5]]],[[[6,7],5],[[7,7],[2,3]]]]
+[[[0,[6,4]],2],[4,[7,[7,5]]]]
+[[[[6,1],[9,1]],[[6,1],9]],[[2,6],0]]
+[[0,[[1,8],[3,5]]],[4,[[8,2],[4,2]]]]
+[[[[9,3],[4,2]],2],[[[2,1],[7,1]],[4,8]]]
+[[[3,[0,2]],3],8]
+[[[4,[4,9]],9],[[[4,4],5],9]]
+[[[[8,2],7],9],[[[1,0],[3,8]],[[7,7],0]]]
+[[[3,2],[9,7]],[[9,[8,2]],[[5,5],3]]]
+[[[7,[3,1]],[[8,3],1]],[[[8,6],[7,0]],4]]
+[[9,[[9,1],5]],[[4,[1,1]],2]]
+[[[[7,4],[0,3]],7],[8,[6,[3,3]]]]
+[5,5]
+[[6,7],[1,[7,[8,1]]]]
+[[1,[0,4]],7]
+[[[4,0],[[0,1],[2,2]]],[9,[[9,9],[3,0]]]]
+[[[6,0],[[8,6],3]],[[5,1],[[8,1],[2,7]]]]
+[[[[8,3],7],5],[9,[[5,1],8]]]
+[[[[4,0],[5,2]],[[0,0],7]],2]
+[[[[0,1],6],2],[[8,2],6]]
+[[[[2,4],1],[[6,7],9]],[[[1,6],9],3]]
+[[5,5],[[8,[7,7]],[5,8]]]
+[[6,[[9,2],[9,7]]],[[[8,5],[4,4]],7]]
+[[[9,[7,7]],[6,0]],[7,[[8,7],[1,2]]]]
+[[7,[6,2]],[[9,[5,2]],[1,4]]]
+[[[7,[5,9]],[[3,9],[4,5]]],[0,6]]
+[[9,[8,[2,2]]],[[9,7],[1,1]]]
+[[[[2,3],4],[[4,8],9]],[[9,[8,6]],[[0,9],0]]]
+[[0,[[9,3],0]],[8,8]]
+[[[[2,9],6],[[2,8],9]],[[[0,5],6],[[6,1],7]]]
+[[9,[[8,3],[5,8]]],[[7,[3,0]],3]]
+[[[4,[4,2]],0],1]
+[[[[9,6],[5,8]],[6,2]],[[[8,0],[7,0]],[[5,6],4]]]
+[[[8,0],[[4,3],[7,4]]],[[3,[7,9]],[[7,3],6]]]
+[[3,[5,[0,3]]],[5,4]]
+[[[[1,2],[6,3]],1],[[7,[5,2]],[[8,8],7]]]
+[[4,[[8,0],[7,1]]],[[8,[8,0]],[[1,5],3]]]
diff --git a/src/day18.rs b/src/day18.rs
new file mode 100644
index 0000000..acd2cf5
--- /dev/null
+++ b/src/day18.rs
@@ -0,0 +1,241 @@
+use std::fmt;
+use std::ops::Add;
+use std::str::FromStr;
+
+#[derive(Clone)]
+enum Value {
+    Number(u32, usize),
+    Pair(Box<Value>, Box<Value>),
+}
+
+impl Value {
+    fn new_pair(left: Value, right: Value) -> Self {
+        Value::Pair(Box::new(left), Box::new(right))
+    }
+}
+
+impl Value {
+    fn is_number_pair(&self) -> bool {
+        match self {
+            Value::Pair(left, right) => left.is_number() && right.is_number(),
+            Value::Number(_, _) => false,
+        }
+    }
+
+    fn is_number(&self) -> bool {
+        matches!(*self, Value::Number(_, _))
+    }
+
+    fn number(&self) -> Option<u32> {
+        match self {
+            Self::Number(n, _) => Some(*n),
+            _ => None
+        }
+    }
+
+    fn index(&self) -> Option<usize> {
+        match self {
+            Self::Number(_, i) => Some(*i),
+            _ => None
+        }
+    }
+
+    fn add_number(&mut self, n: u32) {
+        if let Self::Number(m, i) = self {
+            *self = Value::Number(*m + n, *i);
+        }
+    }
+}
+
+impl Add for Value {
+    type Output = Self;
+
+    fn add(self, other: Self) -> Self {
+        let mut v = Value::new_pair(self, other);
+        reduce(&mut v);
+        v
+    }
+}
+
+fn parse_pair(iter: &mut std::iter::Peekable<std::str::Chars>) -> Value {
+    if iter.next().unwrap() != '[' {
+        panic!();
+    }
+    let left = match iter.peek().unwrap() {
+        '[' => parse_pair(iter),
+        '0'..='9' => Value::Number(iter.next().unwrap().to_digit(10).unwrap(), 0),
+        _ => panic!(),
+    };
+    if iter.next().unwrap() != ',' {
+        panic!();
+    }
+    let right = match iter.peek().unwrap() {
+        '[' => parse_pair(iter),
+        '0'..='9' => Value::Number(iter.next().unwrap().to_digit(10).unwrap(), 0),
+        _ => panic!(),
+    };
+    if iter.next().unwrap() != ']' {
+        panic!();
+    }
+    Value::new_pair(left, right)
+}
+
+impl FromStr for Value {
+    type Err = ();
+
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        let mut v = parse_pair(&mut s.chars().peekable());
+        renumber(&mut v);
+        Ok(v)
+    }
+}
+
+impl fmt::Display for Value {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            Value::Number(n, _) => write!(f, "{}", n),
+            Value::Pair(left, right) => write!(f, "[{},{}]", left, right),
+        }
+    }
+}
+
+fn find_exploded(tree: &Value, depth: usize) -> Option<&Value> {
+    if let Value::Pair(left, right) = tree {
+        if depth == 4 && tree.is_number_pair() {
+            Some(tree)
+        } else {
+            find_exploded(left, depth + 1)
+                .or_else(|| find_exploded(right, depth + 1))
+        }
+    } else {
+        None
+    }
+}
+
+fn find_number(tree: &mut Value, index: usize, n: u32) -> Option<&Value> {
+    match tree {
+        Value::Pair(left, right) => find_number(left, index, n).or_else(|| find_number(right, index, n)),
+        Value::Number(_, i) if *i == index => {
+            tree.add_number(n);
+            Some(tree)
+        },
+        _ => None,
+    }
+}
+
+fn zero_pair(tree: &mut Value, index: usize) {
+    if let Value::Pair(left, right) = tree {
+        if let Value::Pair(ref n, _) = **left {
+            if let Value::Number(_, i) = **n {
+                if i == index {
+                    *left = Box::new(Value::Number(0, 0));
+                    return;
+                }
+            }
+        }
+        if let Value::Pair(ref n, _) = **right {
+            if let Value::Number(_, i) = **n {
+                if i == index {
+                    *right = Box::new(Value::Number(0, 0));
+                    return;
+                }
+            }
+        }
+        zero_pair(left, index);
+        zero_pair(right, index);
+    }
+}
+
+fn renumber_pair(value: &mut Value, counter: &mut usize) {
+    if let Value::Pair(left, right) = value {
+        renumber_pair(left.as_mut(), counter);
+        renumber_pair(right.as_mut(), counter);
+    }
+    if let Value::Number(n, _) = value {
+        *value = Value::Number(*n, *counter);
+        *counter += 1;
+    }
+}
+
+fn renumber(tree: &mut Value) {
+    let mut counter = 0;
+    renumber_pair(tree, &mut counter);
+}
+
+fn explode(tree: &mut Value) {
+    let exploded = &mut find_exploded(tree, 0);
+    if let Some(value) = exploded {
+        if let Value::Pair(left, right) = value {
+            let index = left.index().unwrap();
+            let left_n = left.number().unwrap();
+            let right_n = right.number().unwrap();
+
+            zero_pair(tree, index);
+
+            if index > 0 {
+                find_number(tree, index - 1, left_n);
+            }
+            find_number(tree, index + 2, right_n);
+            renumber(tree);
+        } else {
+            panic!();
+        }
+    }
+}
+
+fn reduce(value: &mut Value) -> &Value {
+    explode(value);
+    value
+}
+
+fn magnitude(value: Value) -> u64 {
+    match value {
+        Value::Number(n, _) => n as u64,
+        Value::Pair(left, right) => 3 * magnitude(*left) + 2 * magnitude(*right),
+    }
+}
+
+fn main() {
+    const INPUT: &str = include_str!("../inputs/day18.txt");
+    let reduced = INPUT
+        .lines()
+        .map(|line| line.parse().unwrap())
+        .reduce(|u: Value, v| u + v)
+        .unwrap();
+    println!("solution {}", magnitude(reduced));
+}
+
+#[test]
+fn test_explode_left() {
+    let mut v: Value = "[[[[[9,8],1],2],3],4]".parse().unwrap();
+    assert_eq!(format!("{}", reduce(&mut v)), "[[[[0,9],2],3],4]");
+}
+
+#[test]
+fn test_explode_right() {
+    let mut v: Value = "[7,[6,[5,[4,[3,2]]]]]".parse().unwrap();
+    assert_eq!(format!("{}", reduce(&mut v)), "[7,[6,[5,[7,0]]]]");
+}
+
+#[test]
+fn test_explode_left_again() {
+    let mut v: Value = "[[6,[5,[4,[3,2]]]],1]".parse().unwrap();
+    assert_eq!(format!("{}", reduce(&mut v)), "[[6,[5,[7,0]]],3]");
+}
+
+#[test]
+fn test_explode() {
+    let mut v: Value = "[[3,[2,[1,[7,3]]]],[6,[5,[4,[3,2]]]]]".parse().unwrap();
+    assert_eq!(
+        format!("{}", reduce(&mut v)),
+        "[[3,[2,[8,0]]],[9,[5,[4,[3,2]]]]]"
+    );
+}
+
+#[test]
+fn test_magnitude() {
+    let v: Value = "[[[[8,7],[7,7]],[[8,6],[7,7]]],[[[0,7],[6,6]],[8,7]]]"
+        .parse()
+        .unwrap();
+    assert_eq!(magnitude(v), 3488);
+}