Day 18
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10
input/18-test.txt
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10
input/18-test.txt
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[[[0,[5,8]],[[1,7],[9,6]]],[[4,[1,2]],[[1,4],2]]]
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[[[5,[2,8]],4],[5,[[9,9],0]]]
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[6,[[[6,2],[5,6]],[[7,6],[4,7]]]]
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[[[6,[0,7]],[0,9]],[4,[9,[9,0]]]]
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[[[7,[6,4]],[3,[1,3]]],[[[5,5],1],9]]
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[[6,[[7,3],[3,2]]],[[[3,8],[5,7]],4]]
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[[[[5,4],[7,7]],8],[[8,3],8]]
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[[9,3],[[9,9],[6,[4,9]]]]
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[[2,[[7,7],7]],[[5,8],[[9,3],[0,2]]]]
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[[[[5,2],5],[8,[3,7]]],[[5,[7,5]],[4,4]]]
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100
input/18.txt
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100
input/18.txt
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[[[[2,8],[4,6]],[[2,4],[9,4]]],[[[0,6],[4,6]],[1,6]]]
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[7,[[5,7],1]]
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[[[[8,8],7],5],[[[5,6],1],6]]
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[[[8,5],[[0,0],[4,9]]],[2,8]]
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[7,[[5,2],[[3,0],[7,7]]]]
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[[6,[6,8]],[3,[5,2]]]
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[6,[[[8,9],[9,9]],[3,8]]]
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[[[1,[0,2]],[7,[3,0]]],8]
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[[9,6],6]
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[[[2,3],1],[9,[3,7]]]
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[5,[[[5,8],3],9]]
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[[[[8,8],3],[2,2]],[2,3]]
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[[[4,9],3],[[[7,3],8],5]]
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[[[3,5],[3,7]],[[[9,7],9],[9,[7,8]]]]
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[[7,1],8]
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[0,[[[6,8],[1,1]],[1,[5,8]]]]
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[[[[2,2],[9,5]],[0,[1,0]]],[4,[[2,4],4]]]
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[[[[2,5],[7,3]],[7,6]],[[6,[4,4]],[3,8]]]
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[[3,[[7,9],2]],[[0,[4,4]],[[6,9],9]]]
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[[[7,7],[[1,4],[1,6]]],[7,[[6,3],6]]]
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[[0,8],[[[1,6],2],4]]
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[[0,[[2,7],[0,4]]],[[[3,8],[7,7]],5]]
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[[[[9,9],[1,3]],[9,[4,3]]],[[[3,4],[6,4]],1]]
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[[[9,[0,9]],[2,[7,6]]],[2,[[1,9],[3,3]]]]
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[[4,[5,6]],[[[1,5],6],[[1,5],[5,2]]]]
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[1,[[3,[2,1]],5]]
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[[4,[3,8]],[3,[6,3]]]
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[[7,1],[[3,[6,0]],[5,[1,1]]]]
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[[8,7],[[[0,1],[2,6]],[5,[4,7]]]]
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[9,[[[1,6],[8,9]],[6,6]]]
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[4,9]
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[[[[0,8],[8,5]],9],[7,[1,3]]]
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[[[[8,5],0],[[4,6],4]],[8,4]]
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[[[[8,9],8],[[3,1],[7,6]]],2]
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[[[[6,3],0],[2,[4,8]]],[[[0,3],[3,5]],4]]
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[0,[[9,[0,6]],5]]
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[[[[1,9],[2,7]],[[4,0],[9,9]]],[[8,[3,6]],[3,4]]]
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[[[[0,7],[8,4]],1],[[8,3],[[3,5],[8,0]]]]
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[[[[3,5],4],[0,9]],[[[1,7],5],[9,[8,0]]]]
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[[[8,[6,8]],[[3,7],[0,8]]],[[[5,2],[1,7]],[9,5]]]
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[[[[5,1],[0,7]],4],[0,4]]
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[[[[9,8],[3,9]],[[0,6],3]],[[[9,1],[8,7]],2]]
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[[9,[[0,3],6]],[[3,4],[[8,9],5]]]
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[[1,[1,8]],[[6,[4,2]],1]]
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[7,[[1,[5,2]],[[9,7],0]]]
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[0,[8,6]]
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[1,4]
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[[8,[4,1]],[[[4,0],[0,0]],[7,[3,4]]]]
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[2,[[1,[1,8]],[[3,4],1]]]
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[[8,[[1,2],[3,1]]],[[[4,4],[7,9]],1]]
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[[4,[0,[6,4]]],[9,[0,[1,2]]]]
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[[6,[3,1]],[[7,8],[8,[2,5]]]]
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[[[2,[3,3]],[[6,4],[9,4]]],[[[1,5],[7,4]],[0,6]]]
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[[[[8,0],3],[[4,0],3]],[[7,5],4]]
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[[[2,[4,3]],[[2,1],5]],1]
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[[[8,1],[0,4]],[9,[[1,4],[9,0]]]]
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[[[5,0],[[7,7],9]],[[6,[6,2]],7]]
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[[[[5,9],0],[[4,6],[3,8]]],[6,[6,5]]]
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[[[6,[7,8]],[5,3]],[[3,[6,5]],[[8,7],[4,7]]]]
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[[9,[[8,7],4]],[[[6,3],0],[[2,3],[5,9]]]]
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[[[[1,8],6],1],[[[7,8],4],[7,2]]]
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[[[[7,1],[6,2]],[[7,8],2]],0]
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[[[4,5],[0,3]],[[2,4],1]]
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[[[9,1],7],[[[8,8],[0,7]],[8,0]]]
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[[5,[[7,5],[7,5]]],[3,[4,8]]]
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[[7,[1,0]],[[3,[1,5]],0]]
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[[[5,1],[[5,2],[7,3]]],[[7,[3,9]],9]]
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[5,[1,[[9,9],[3,0]]]]
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[[2,0],[9,[6,[3,3]]]]
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[[[[0,4],[4,8]],[[1,9],[5,8]]],[[[7,0],5],[5,1]]]
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[[[[1,5],[9,2]],[6,[3,6]]],[4,[1,[1,5]]]]
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[[[[1,4],[4,6]],[[5,5],[3,5]]],[[[7,1],4],[[0,7],4]]]
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[[6,[3,5]],1]
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[8,[[1,[0,7]],[[2,5],6]]]
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[[[[1,6],3],[[9,7],9]],[[7,8],3]]
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[[[[9,9],[2,0]],0],[1,4]]
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[[[[1,3],[5,1]],[[0,4],2]],0]
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[[3,2],[7,[[9,3],8]]]
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[[9,0],[4,[[8,7],[5,5]]]]
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[[[[7,4],8],[[4,4],1]],9]
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[[9,[[7,9],1]],[[[6,5],7],[[2,5],2]]]
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[7,2]
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[[[6,6],[[9,4],4]],6]
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[[1,[[5,0],3]],[5,[4,4]]]
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[[[3,2],[[4,6],6]],[[3,[9,5]],[[0,2],[4,6]]]]
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[5,[[0,[3,0]],[7,[7,9]]]]
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[[[[0,4],[1,5]],4],[8,[[4,7],8]]]
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[[[[9,1],0],0],4]
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[[[[8,4],[4,2]],[9,[1,7]]],[6,3]]
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[2,[[[8,3],2],[[3,1],8]]]
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[[[[9,0],[7,8]],[[2,7],[0,3]]],[[[8,5],3],[9,[6,8]]]]
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[[[[8,9],[9,1]],[4,[0,1]]],[[[7,8],2],2]]
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[[[[2,2],[4,1]],[2,[2,8]]],[[[6,5],1],9]]
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[[[[3,0],7],7],[[[9,3],7],4]]
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[[[[7,5],1],3],[[[0,7],7],[[2,6],[9,9]]]]
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[[[[5,2],8],[9,[8,8]]],[2,[[0,8],[5,6]]]]
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[[[[7,7],[1,2]],[6,6]],[8,[5,8]]]
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[[7,[4,[8,9]]],[[4,[7,2]],8]]
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[[[6,4],[7,7]],[[[3,7],0],[0,1]]]
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[[1,[5,9]],[8,[4,6]]]
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258
src/bin/18.rs
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258
src/bin/18.rs
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use std::ops::Add;
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fn main() {
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println!(
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"First solution: {}",
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part1(include_str!("../../input/18.txt"))
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);
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println!(
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"Second solution: {}",
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part2(include_str!("../../input/18.txt"))
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);
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}
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fn part1(s: &str) -> u32 {
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s.lines()
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.map(Number::from)
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.reduce(|a, b| a + b)
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.unwrap()
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.magnitude()
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}
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fn part2(s: &str) -> u32 {
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let numbers: Vec<Number> = s.lines().map(Number::from).collect();
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let mut max = 0;
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for a in &numbers {
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for b in &numbers {
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let sum = (a.clone() + b.clone()).magnitude();
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max = max.max(sum);
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}
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}
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max
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}
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#[derive(Debug, Clone, Eq)]
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struct Number(Vec<Token>);
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#[derive(Debug, Clone, Copy, PartialEq, Eq)]
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enum Token {
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Open,
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Close,
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Num(u32),
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}
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impl Token {
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/// assume that this token is a number and return the value or panic.
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fn num(&self) -> u32 {
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match self {
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Token::Num(n) => *n,
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t => panic!("expected Token::Num, but got {:?}", t),
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}
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}
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fn num_mut(&mut self) -> &mut u32 {
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match self {
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Token::Num(n) => n,
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t => panic!("expected Token::Num, but got {:?}", t),
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}
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}
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}
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impl Add for Number {
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type Output = Number;
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fn add(self, rhs: Self) -> Self::Output {
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let mut v = vec![Token::Open];
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v.extend(self.0);
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v.extend(rhs.0);
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v.push(Token::Close);
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Self(v).reduce()
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}
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}
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impl From<&str> for Number {
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fn from(s: &str) -> Self {
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Self(
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s.chars()
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.filter_map(|c| match c {
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'[' => Some(Token::Open),
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']' => Some(Token::Close),
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',' => None, // commas do not matter after parsing
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d => match d.to_digit(10) {
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Some(d) => Some(Token::Num(d)),
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None => panic!("unknown char '{}'", d),
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},
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})
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.collect(),
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)
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}
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}
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impl PartialEq for Number {
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fn eq(&self, other: &Self) -> bool {
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self.0 == other.0
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}
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}
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impl Number {
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fn magnitude(&self) -> u32 {
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let mut stack: Vec<u32> = Vec::new();
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for tok in &self.0 {
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match tok {
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Token::Open => continue,
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Token::Close => {
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let b = stack.pop().unwrap();
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let a = stack.pop().unwrap();
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stack.push(3 * a + 2 * b);
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}
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Token::Num(n) => stack.push(*n),
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}
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}
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stack.pop().unwrap()
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}
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fn reduce(&self) -> Self {
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let mut result = self.clone();
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loop {
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let (num, exploded) = result.explode();
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if exploded {
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result = num;
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} else {
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let (num, split) = num.split();
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if split {
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result = num;
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} else {
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return result;
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}
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}
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}
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}
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/// Perform the leftmost explosion, if any. Returns true if any explosions happened.
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fn explode(&self) -> (Self, bool) {
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let mut explode_happened = false;
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let mut depth = 0;
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// Keep track of the last num to move a value backwards.
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let mut last_num_idx: Option<usize> = None;
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// Carry a value to the next num
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let mut carrying: Option<u32> = None;
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let mut result: Vec<Token> = Vec::new();
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let mut tokens = self.0.iter().copied();
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while let Some(tok) = tokens.next() {
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match tok {
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Token::Open if depth >= 4 && !explode_happened => {
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// Explode!
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explode_happened = true;
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let left = tokens.next().unwrap().num();
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let right = tokens.next().unwrap().num();
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let _close = tokens.next();
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if let Some(i) = last_num_idx {
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*result[i].num_mut() += left;
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}
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carrying = Some(right);
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result.push(Token::Num(0));
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}
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Token::Open => {
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depth += 1;
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result.push(Token::Open);
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}
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Token::Close => {
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depth -= 1;
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result.push(Token::Close);
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}
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Token::Num(n) => {
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last_num_idx = Some(result.len());
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let n = n + carrying.take().unwrap_or(0);
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result.push(Token::Num(n));
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}
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}
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}
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(Self(result), explode_happened)
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}
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/// Perform the leftmost split, if any. Returns true if any splits happened.
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fn split(&self) -> (Self, bool) {
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let mut split_happened = false;
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let mut result = Vec::new();
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for tok in self.0.iter().copied() {
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match tok {
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Token::Num(n) if n > 9 && !split_happened => {
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// Split!
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split_happened = true;
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let (a, b) = split(n);
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result.extend([Token::Open, Token::Num(a), Token::Num(b), Token::Close]);
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}
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tok => result.push(tok),
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}
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}
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(Self(result), split_happened)
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}
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}
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fn split(n: u32) -> (u32, u32) {
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if n % 2 == 0 {
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(n / 2, n / 2)
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} else {
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(n / 2, n / 2 + 1)
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}
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}
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#[cfg(test)]
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mod test {
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use crate::{part1, part2, Number};
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#[test]
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fn magnitude() {
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assert_eq!(Number::from("[[1,2],[[3,4],5]]").magnitude(), 143);
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assert_eq!(
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Number::from("[[[[0,7],4],[[7,8],[6,0]]],[8,1]]").magnitude(),
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1384
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);
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assert_eq!(
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Number::from("[[[[1,1],[2,2]],[3,3]],[4,4]]").magnitude(),
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445
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);
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assert_eq!(
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Number::from("[[[[3,0],[5,3]],[4,4]],[5,5]]").magnitude(),
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791
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);
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assert_eq!(
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Number::from("[[[[5,0],[7,4]],[5,5]],[6,6]]").magnitude(),
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1137
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);
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assert_eq!(
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Number::from("[[[[8,7],[7,7]],[[8,6],[7,7]]],[[[0,7],[6,6]],[8,7]]]").magnitude(),
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3488
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);
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}
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#[test]
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fn explode() {
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let expected = Number::from("[[[[0,9],2],3],4]");
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let actual = Number::from("[[[[[9,8],1],2],3],4]").reduce();
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assert_eq!(expected, actual)
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}
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#[test]
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fn example_part1() {
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assert_eq!(part1(include_str!("../../input/18-test.txt")), 4140);
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}
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#[test]
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fn example_part2() {
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assert_eq!(part2(include_str!("../../input/18-test.txt")), 3993);
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}
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}
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