day7, part2

day07/src/main.rs

@@ -3,7 +3,7 @@ use std::collections::HashSet;
 use winnow::{
     PResult, Parser,
     ascii::{dec_uint, newline, space1},
-    combinator::{eof, opt, separated, separated_pair, seq},
+    combinator::{opt, separated, separated_pair, seq},
 };
 
 fn main() {
@@ -16,16 +16,21 @@ fn pt1(input: &str) -> u64 {
     let mut total = 0;
     let eqs = parse(input);
     for eq in &eqs {
-        if check(eq) {
+        if check(eq, false) {
             total += eq.total;
         }
     }
     total
 }
 
-fn pt2(_input: &str) -> u64 {
+fn pt2(input: &str) -> u64 {
     let mut total = 0;
-
+    let eqs = parse(input);
+    for eq in &eqs {
+        if check(eq, true) {
+            total += eq.total;
+        }
+    }
     total
 }
 
@@ -46,7 +51,7 @@ impl Equation {
     }
 }
 
-fn check(equation: &Equation) -> bool {
+fn check(equation: &Equation, pt2: bool) -> bool {
     let mut processed = HashSet::new();
     let mut q = Vec::new();
     let target = equation.total;
@@ -71,10 +76,17 @@ fn check(equation: &Equation) -> bool {
                 process_top = false;
                 q.push(plus);
             }
+            if pt2 {
+                let concat = (next_idx, cat(cur_val, next_val));
+                if concat.1 <= target && !processed.contains(&concat) {
+                    process_top = false;
+                    q.push(concat);
+                }
+            }
         }
         if process_top {
             let _ = q.pop();
-            if cur_val == target {
+            if cur_val == target && cur_idx == (equation.factors.len() - 1) {
                 return true;
             }
             processed.insert(current);
@@ -84,6 +96,10 @@ fn check(equation: &Equation) -> bool {
     false
 }
 
+fn cat(a: u64, b: u64) -> u64 {
+    format!("{a}{b}").parse().unwrap()
+}
+
 fn parse_equation(input: &mut &str) -> PResult<Equation> {
     let (total, factors) = separated_pair(
         dec_uint,
@@ -96,12 +112,10 @@ fn parse_equation(input: &mut &str) -> PResult<Equation> {
 }
 
 fn parse(input: &str) -> Vec<Equation> {
-    let (equations, _): (Vec<Equation>, _) = seq!(
+    let (equations, _): (Vec<Equation>, _) =
-        separated(1.., parse_equation, newline),
+        seq!(separated(1.., parse_equation, newline), opt(newline))
-        seq!(opt(newline), opt(eof))
+            .parse(input)
-    )
+            .unwrap();
-    .parse(input)
-    .unwrap();
     equations
 }
 
@@ -127,6 +141,6 @@ mod test {
 
     #[test]
     fn p2() {
-        assert_eq!(0, pt2(TEST_INPUT));
+        assert_eq!(11387, pt2(TEST_INPUT));
     }
 }