2020 day 18

2020/18/part2.js

@@ -0,0 +1,32 @@
+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))
+    )
+  }
+  // if there's addition, do that
+  while (expression.match(/\+/)){
+    expression = expression.replace(/(\d+) \+ (\d+)/, (match, a, b) => 
+      parseInt(a) + parseInt(b)
+    )
+  }
+  // if there's multiplication, do that
+  while (expression.match(/\*/)) {
+    expression = expression.replace(/(\d+) \* (\d+)/, (match, a, b) => 
+      parseInt(a) * parseInt(b)
+    )
+  }
+  return Number(expression)
+}
+
+let runningTotal = 0
+for (expression of expressions) {
+  runningTotal += calc (expression)
+}
+console.log(runningTotal)