From 132ab771e85c656b260ca5a20767b5313dfa0ac7 Mon Sep 17 00:00:00 2001
From: Joe Hildebrand <joe-github@cursive.net>
Date: Sat, 7 Dec 2024 12:46:35 -0700
Subject: [PATCH] Cleanup

---
 day7.ts | 62 ++++++++++++++++++++++++++-------------------------------
 t       |  9 +++++++++
 2 files changed, 37 insertions(+), 34 deletions(-)
 create mode 100644 t

diff --git a/day7.ts b/day7.ts
index 1b0f5fe..24aeff3 100644
--- a/day7.ts
+++ b/day7.ts
@@ -1,57 +1,51 @@
 import { type MainArgs, parseFile } from './lib/utils.ts';
 
-type Parsed = [number, number[]][];
+type Line = [number, number[]];
+type Parsed = Line[];
 
 // Starting from the front of the reversed list (the endq), see if we can rule
 // out any of the operations
-function calc(left: number, operands: number[], concat = false): number {
-  if ((left <= 0) || (Math.floor(left) !== left) || !operands.length) {
-    return left;
+function calc(left: number, operands: number[], concat = false): boolean {
+  if (!operands.length) {
+    return left === 0;
   }
   const [first, ...rest] = operands;
-  if (concat) { // Part 2
-    // This is most likely to rule out an operand.
-    // 20 || 123 = 20123.  The opposite op is 20123 -- 123, which fails if
-    // LHS doesn't end in RHS, then truncates.
-    const sfirst = String(first);
+  if (concat) { // Part 2 adds concatenation operator
     const sleft = String(left);
-    if (sleft.endsWith(sfirst)) {
-      if (calc(Number(sleft.slice(0, -sfirst.length)), rest, true) === 0) {
-        return 0;
-      }
+    const sfirst = String(first);
+    const prefix = sleft.slice(0, -sfirst.length)
+    if ((prefix + sfirst === sleft) && calc(Number(prefix), rest, concat)) {
+      return true;
     }
   }
-  if (calc(left - first, rest, concat) === 0) {
-    return 0;
-  };
-  if (calc(left / first, rest, concat) === 0) {
-    return 0;
+
+  const dleft = left / first;
+  if (Number.isInteger(dleft) && calc(dleft, rest, concat)) {
+    return true;
   }
-  return left;
+
+  const mleft = left - first;
+  return (mleft >= 0) && calc(mleft, rest, concat);
 }
 
 function part1(inp: Parsed): number {
-  let sum = 0;
-  for (const [tot, operands] of inp) {
-    if (calc(tot, operands.reverse()) === 0) {
-      sum += tot;
-    }
-  }
-  return sum;
+  return inp.reduce(
+    (t, [tot, operands]) => t + (calc(tot, operands) ? tot : 0),
+    0
+  );
 }
 
 function part2(inp: Parsed): number {
-  let sum = 0;
-  for (const [tot, operands] of inp) {
-    // Already reversed
-    if (calc(tot, operands, true) === 0) {
-      sum += tot;
-    }
-  }
-  return sum;
+  return inp.reduce(
+    (t, [tot, operands]) => t + (calc(tot, operands, true) ? tot : 0),
+    0
+  );
 }
 
 export default async function main(args: MainArgs): Promise<[number, number]> {
   const inp = await parseFile<Parsed>(args);
+  for (const [_tot, operands] of inp) {
+    operands.reverse();
+  }
   return [part1(inp), part2(inp)];
 }
diff --git a/t b/t
new file mode 100644
index 0000000..fc6e099
--- /dev/null
+++ b/t
@@ -0,0 +1,9 @@
+190: 10 19
+3267: 81 40 27
+83: 17 5
+156: 15 6
+7290: 6 8 6 15
+161011: 16 10 13
+192: 17 8 14
+21037: 9 7 18 13
+292: 11 6 16 20