Day 18

Author: Chris Poch

18-1.txt

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+1 + 2 * 3 + 4 * 5 + 6

18-2.txt

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+1 + (2 * 3) + (4 * (5 + 6))

18-3.txt

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+2 * 3 + (4 * 5)
+5 + (8 * 3 + 9 + 3 * 4 * 3)
+5 * 9 * (7 * 3 * 3 + 9 * 3 + (8 + 6 * 4))
+((2 + 4 * 9) * (6 + 9 * 8 + 6) + 6) + 2 + 4 * 2

18.py

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+import os
+import sys
+
+debug = True
+
+fileName = ""
+try:
+    fileName = sys.argv[1]
+    if len(fileName) < 1:
+        fileName = "18.txt"
+except:
+    fileName = "18.txt"
+if debug:
+    print(fileName)
+
+def solve(lines, precedence):
+    solutions = []
+    for line in lines:
+        #convert to reverse polish notation
+        result = ""
+        stack = []
+        for char in line:
+            if char.isdigit():
+                result += char
+            if char == "(":
+                stack.append(char)
+            if char == ")":
+                while len(stack) > 0 and stack[-1] != "(":
+                    result += stack.pop()
+                stack.pop()
+            if char == "+" or char == "*":
+                while len(stack) > 0 and stack[-1] != "(" and precedence[char] <= precedence[stack[-1]]:
+                    result += stack.pop()
+                stack.append(char)
+        while len(stack) > 0:
+            result += stack.pop()
+
+        #evaluate reverse polish notation to an int
+        stack = []
+        for char in result:
+            if char.isdigit():
+                stack.append(int(char))
+            if char == "+" or char == "*":
+                result = 0
+                two = stack.pop()
+                one = stack.pop()
+                if char == "+":
+                    result = int(one) + int(two)
+                else:
+                    result = int(one) * int(two)
+                stack.append(result)
+        solutions.append(stack[0])
+    return solutions
+
+with open(fileName) as file:
+    lines = file.readlines()
+
+    solutions = solve(lines, {"+":1,"*":1}) 
+    if debug:
+        print(solutions)
+    total = 0
+    for sol in solutions:
+        total += sol
+    print("part 1", total) #part 1
+
+    solutions = solve(lines, {"+":2,"*":1}) 
+    if debug:
+        print(solutions)
+    total = 0
+    for sol in solutions:
+        total += sol
+    print("part 2", total) #part 2