2020 day 18

2020/18/part1.js

@@ -0,0 +1,26 @@
+const fs = require('fs');
+const expressions = fs.readFileSync('./input.txt', 'utf-8').split('\n');
+
+function calc (expression) {
+  // if it's just a number, do nothing
+  if (!isNaN(Number(expression))) { Number(expression) }
+  // if there's brackets, do that first
+  while (expression.match(/\(/)){
+    expression = expression.replace(/\([^()]+\)/, match => 
+      calc (match.slice(1, match.length-1))
+    )
+  }
+  // do all the calculations until it's just a number
+  while (isNaN(Number(expression))) {
+    expression = expression.replace(/(\d+) ([+*]) (\d+)/, (match, a, op, b) => 
+      op == '+' ? parseInt(a) + parseInt(b) : parseInt(a) * parseInt(b)
+    )
+  }
+  return Number(expression)
+}
+
+let runningTotal = 0
+for (expression of expressions) {
+  runningTotal += calc (expression)
+}
+console.log(runningTotal)