Day 18

day18/part1.py

@@ -0,0 +1,31 @@
+#!/usr/bin/env python3
+import re
+
+lines = (x.strip().replace(" ", "") for x in open("input.txt"))
+RE_PLUS = re.compile(r"\+")
+RE_MUL = re.compile(r"\*")
+RE_NUM = re.compile(r"^\d")
+RE_PAR = re.compile(r"^\((.*?)\)$")
+
+def evaluate(line):
+    stack = [0]
+    num = 0
+    op = ['+']
+    for char in line:
+        if char in '+*':
+            stack[-1] = stack[-1]*num if op[-1] == '*' else stack[-1]+num
+            op[-1] = char
+            num = 0
+        elif char == '(':
+            stack.append(0)
+            op.append('+')
+        elif char == ')':
+            stack[-1] = stack[-1]*num if op[-1] == '*' else stack[-1]+num
+            num = stack.pop()
+            op.pop()
+        else:
+            num = num*10 + int(char)
+    stack[-1] = stack[-1]*num if op[-1] == '*' else stack[-1]+num
+    return stack[0]
+
+print(sum(evaluate(line) for line in lines))