Added day 18 part2

src/bin/day18.rs

@@ -3,23 +3,21 @@ use std::fs::File;
 use std::io::{self, BufRead};
 use std::vec::Vec;
 
-fn extract_paren_expression(input: &str) -> String {
-    let mut res: String = "".to_string();
-    let mut open_count = 1;
+fn read_paren_expression(input: &str) -> (&str, &str) {
+    let mut open_count = 0;
     let mut close_count = 0;
 
-    for c in input[1..].chars() {
-        match c {
+    for i in 0..input.len() {
+        match input.chars().nth(i).unwrap() {
             '(' => open_count += 1,
             ')' => {
                 close_count += 1;
                 if open_count == close_count {
-                    return res;
+                    return (&input[1..i], &input[i + 1..]);
                 }
             }
             _ => {}
         }
-        res += &c.to_string();
     }
 
     panic!(
@@ -28,40 +26,114 @@ fn extract_paren_expression(input: &str) -> String {
     );
 }
 
-fn extract_number(input: &str) -> String {
-    input.chars().take_while(|c| c.is_ascii_digit()).collect()
+fn read_number(input: &str) -> (&str, &str) {
+    for i in 0..input.len() {
+        if !input.chars().nth(i).unwrap().is_ascii_digit() {
+            return (&input[0..i], &input[i..]);
+        }
+    }
+    return (input, "");
 }
 
-fn eval_expression(input: &str) -> u64 {
-    let mut clean: String = input.chars().filter(|c| *c != ' ').collect();
-    let mut res = 0;
-    let mut op = '^';
+#[derive(PartialEq, Clone, Debug)]
+enum Expression {
+    Num(u64),
+    OpAdd,
+    OpMul,
+    SubExpr(Vec<Expression>),
+}
 
-    while clean != "" {
-        let c = clean.chars().nth(0).unwrap();
+fn parse_expression(input: &str) -> Vec<Expression> {
+    let mut expr = Vec::new();
+    let mut rest = input;
+
+    while rest != "" {
+        let c = rest.chars().nth(0).unwrap();
         if c.is_ascii_digit() {
-            let substr = extract_number(&clean);
-            clean = clean[substr.len()..].to_string();
-            let num: u64 = substr.parse().unwrap();
-            match op {
-                '^' => res = num,
-                '+' => res += num,
-                '*' => res *= num,
-                _ => panic!("Unsupported Op: {}", op),
-            }
-        } else if c == '+' || c == '*' {
-            op = c;
-            clean = clean[1..].to_string();
+            let (substr, tail) = read_number(rest);
+            expr.push(Expression::Num(substr.parse().unwrap()));
+            rest = tail;
         } else if c == '(' {
-            let substr = extract_paren_expression(&clean);
-            clean = clean[substr.len() + 2..].to_string();
-            let num = eval_expression(&substr);
-            match op {
-                '^' => res = num,
-                '+' => res += num,
-                '*' => res *= num,
-                _ => panic!("Unsupported Op: {}", op),
+            let (substr, tail) = read_paren_expression(rest);
+            expr.push(Expression::SubExpr(parse_expression(substr)));
+            rest = tail;
+        } else if c == '+' {
+            expr.push(Expression::OpAdd);
+            rest = &rest[1..];
+        } else if c == '*' {
+            expr.push(Expression::OpMul);
+            rest = &rest[1..];
+        } else {
+            rest = &rest[1..];
+        }
+    }
+
+    expr
+}
+
+fn eval_part1(expr: &Vec<Expression>) -> u64 {
+    let subexpr_eval = expr.iter().map(|e| match e {
+        Expression::SubExpr(subexpr) => Expression::Num(eval_part1(subexpr)),
+        _ => e.clone(),
+    });
+
+    let mut res = 0;
+    let mut op = Expression::OpAdd;
+    for e in subexpr_eval {
+        match e {
+            Expression::Num(n) => match op {
+                Expression::OpAdd => res += n,
+                Expression::OpMul => res *= n,
+                _ => panic!("Malformed expression. Not an op."),
+            },
+            Expression::OpAdd => op = Expression::OpAdd,
+            Expression::OpMul => op = Expression::OpMul,
+            _ => panic!("Malformed expression."),
+        }
+    }
+
+    res
+}
+
+fn eval_part2(expr: &Vec<Expression>) -> u64 {
+    let subexpr_eval: Vec<Expression> = expr
+        .iter()
+        .map(|e| match e {
+            Expression::SubExpr(subexpr) => Expression::Num(eval_part2(subexpr)),
+            _ => e.clone(),
+        })
+        .collect();
+
+    let mut mul_eval: Vec<Expression> = Vec::new();
+    let mut i = 0;
+    while i < subexpr_eval.len() {
+        match subexpr_eval[i] {
+            Expression::OpAdd => {
+                if let Expression::Num(n1) = mul_eval.pop().unwrap() {
+                    if let Expression::Num(n2) = subexpr_eval[i + 1] {
+                        mul_eval.push(Expression::Num(n1 + n2));
+                        i += 2;
+                    } else {
+                        panic!("Malformed expression: Expected Number")
+                    }
+                } else {
+                    panic!("Malformed expression: Expected Number")
+                }
             }
+            _ => {
+                mul_eval.push(subexpr_eval[i].clone());
+                i += 1;
+            }
+        }
+    }
+
+    let mut res = 1;
+
+    for e in mul_eval {
+        match e {
+            Expression::Num(n) => res *= n,
+            Expression::OpMul => {}
+            _ => panic!("Malformed expression."),
         }
     }
 
@@ -72,8 +144,15 @@ fn main() -> Result<(), Box<dyn Error>> {
     let file = File::open("inputs/day18.txt")?;
     let lines = io::BufReader::new(file).lines().map(|l| l.unwrap());
 
-    let res = lines.map(|l| eval_expression(&l)).fold(0, |x, y| x + y);
-    println!("Answer: {}", res);
+    let exprs: Vec<Vec<Expression>> = lines.map(|l| parse_expression(&l)).collect();
+
+    let result1 = exprs.iter().map(|e| eval_part1(e)).fold(0, |x, y| x + y);
+
+    println!("Answer Part 1: {}", result1);
+
+    let result2 = exprs.iter().map(|e| eval_part2(e)).fold(0, |x, y| x + y);
+
+    println!("Answer Part 2: {}", result2);
 
     Ok(())
 }
@@ -83,31 +162,97 @@ mod tests {
     use crate::*;
 
     #[test]
-    fn test_extractor() {
+    fn test_paren_expression() {
         assert_eq!(
-            extract_paren_expression("((2 + 4 * 9) * (6 + 9 * 8 + 6) + 6) + 2 + 4 * 2"),
-            "(2 + 4 * 9) * (6 + 9 * 8 + 6) + 6"
+            read_paren_expression("((2 + 4 * 9) * (6 + 9 * 8 + 6) + 6) + 2 + 4 * 2"),
+            ("(2 + 4 * 9) * (6 + 9 * 8 + 6) + 6", " + 2 + 4 * 2")
         );
     }
 
     #[test]
-    fn test_basics() {
-        assert_eq!(eval_expression("23"), 23);
-        assert_eq!(eval_expression("2 + 3 * 4"), 20);
-        assert_eq!(eval_expression("2 + (3 * 4)"), 14);
+    fn test_number() {
+        assert_eq!(read_number("243 + 3"), ("243", " + 3"),);
     }
 
     #[test]
-    fn test_problems() {
-        assert_eq!(eval_expression("2 * 3 + (4 * 5)"), 26);
-        assert_eq!(eval_expression("5 + (8 * 3 + 9 + 3 * 4 * 3)"), 437);
+    fn test_parse() {
+        assert_eq!(parse_expression("23"), vec![Expression::Num(23)]);
         assert_eq!(
-            eval_expression("5 * 9 * (7 * 3 * 3 + 9 * 3 + (8 + 6 * 4))"),
+            parse_expression("2 + 3 * 4"),
+            vec![
+                Expression::Num(2),
+                Expression::OpAdd,
+                Expression::Num(3),
+                Expression::OpMul,
+                Expression::Num(4)
+            ]
+        );
+        assert_eq!(
+            parse_expression("2 + (3 * 4)"),
+            vec![
+                Expression::Num(2),
+                Expression::OpAdd,
+                Expression::SubExpr(vec![
+                    Expression::Num(3),
+                    Expression::OpMul,
+                    Expression::Num(4)
+                ])
+            ]
+        );
+    }
+
+    #[test]
+    fn test_basics1() {
+        assert_eq!(eval_part1(&parse_expression("23")), 23);
+        assert_eq!(eval_part1(&parse_expression("2 + 3 * 4")), 20);
+        assert_eq!(eval_part1(&parse_expression("2 + (3 * 4)")), 14);
+    }
+
+    fn test_basics2() {
+        assert_eq!(eval_part2(&parse_expression("23")), 23);
+        assert_eq!(eval_part2(&parse_expression("2 + 3 * 2 * 3 + 2")), 50);
+        assert_eq!(eval_part2(&parse_expression("2 + (3 * 4)")), 14);
+    }
+
+    #[test]
+    fn test_problems1() {
+        assert_eq!(eval_part1(&parse_expression("2 * 3 + (4 * 5)")), 26);
+        assert_eq!(
+            eval_part1(&parse_expression("5 + (8 * 3 + 9 + 3 * 4 * 3)")),
+            437
+        );
+        assert_eq!(
+            eval_part1(&parse_expression(
+                "5 * 9 * (7 * 3 * 3 + 9 * 3 + (8 + 6 * 4))"
+            )),
             12240
         );
         assert_eq!(
-            eval_expression("((2 + 4 * 9) * (6 + 9 * 8 + 6) + 6) + 2 + 4 * 2"),
+            eval_part1(&parse_expression(
+                "((2 + 4 * 9) * (6 + 9 * 8 + 6) + 6) + 2 + 4 * 2"
+            )),
             13632
         );
     }
+
+    #[test]
+    fn test_problems2() {
+        assert_eq!(eval_part2(&parse_expression("2 * 3 + (4 * 5)")), 46);
+        assert_eq!(
+            eval_part2(&parse_expression("5 + (8 * 3 + 9 + 3 * 4 * 3)")),
+            1445
+        );
+        assert_eq!(
+            eval_part2(&parse_expression(
+                "5 * 9 * (7 * 3 * 3 + 9 * 3 + (8 + 6 * 4))"
+            )),
+            669060
+        );
+        assert_eq!(
+            eval_part2(&parse_expression(
+                "((2 + 4 * 9) * (6 + 9 * 8 + 6) + 6) + 2 + 4 * 2"
+            )),
+            23340
+        );
+    }
 }