Day 18

challenges/2020/18.js

@@ -0,0 +1,83 @@
+const getSum = (stack) => stack.reduce((acc, v) => acc + v);
+
+const getProduct = (stack) => stack.reduce((acc, v) => acc * v);
+
+const workStack = (num, stack, operator, favorAddition = false) => {
+  if (operator === '+') {
+    stack.push((stack.pop() || 0) + num);
+  } else if (operator === '*' && favorAddition) {
+    stack.push(num);
+  } else {
+    stack.push((stack.pop() || 0) * num);
+  }
+};
+
+const evaluate = (input, reducer, favorAddition = false) => {
+  input = input.split('\n').map((line) => line.replace(/\s+/g, ''));
+  let sum = 0;
+
+  const calculate = (expression, i = 0) => {
+    let currOperator = '+';
+    let subSum, newIdx;
+    const stack = [];
+
+    while (i < expression.length) {
+      const op = expression[i];
+
+      switch (op) {
+        case '+':
+          currOperator = '+';
+          break;
+
+        case '*':
+          currOperator = '*';
+          break;
+
+        case '(':
+          [subSum, newIdx] = calculate(expression, i + 1);
+          workStack(subSum, stack, currOperator, favorAddition);
+          i = newIdx;
+          break;
+
+        case ')':
+          return [reducer(stack), i];
+
+        default:
+          workStack(Number(op), stack, currOperator, favorAddition);
+      }
+      i += 1;
+    }
+    return [reducer(stack)];
+  };
+
+  for (let expression of input) {
+    sum += calculate(expression)[0];
+  }
+  return sum;
+};
+
+/**
+ * Part 1
+ */
+const solvePuzzle = (input) => evaluate(input, getSum, false);
+
+/**
+ * Part 2
+ */
+const solvePuzzle2 = (input) => evaluate(input, getProduct, true);
+
+// eslint-disable-next-line no-undef
+test('Puzzle Result', (done) => {
+  const fs = require('fs');
+  const path = require('path');
+  const currentDay = path.basename(__filename).split('.')[0];
+
+  fs.readFile(`${__dirname}/inputs/${currentDay}.txt`, (err, input) => {
+    if (err) {
+      throw err;
+    }
+    const result = solvePuzzle(input.toString());
+    console.log('\x1b[1m\x1b[31m%s\x1b[0m', 'Result:', result);
+    done();
+  });
+});