2024(2): solve puzzle 1

2024/2/1.py

@@ -0,0 +1,21 @@
+verbose = True
+
+safe = 0
+unsafe = 0
+with open("input", "r") as fp:
+	while line := fp.readline():
+		nums = list(map(int, line.split(" ")))
+		increasing = (nums[1] - nums[0]) > 0
+		for i in range(1, len(nums)):
+			diff = nums[i] - nums[i - 1]
+			if abs(diff) > 3 or abs(diff) == 0 or increasing != (diff > 0):
+				unsafe += 1
+				if verbose:
+					print(f"unsafe: {line}", end="")
+				break
+		else:
+			safe += 1
+			if verbose:
+				print(f"  safe: {line}", end="")
+
+print(f"Found {safe} safe and {unsafe} unsafe reports.")

2024/2/README.md

@@ -26,15 +26,42 @@ The engineers are trying to figure out which reports are *safe*. The Red-Nosed r
 
 In the example above, the reports can be found safe or unsafe by checking those rules:
 
-    `7 6 4 2 1`: *Safe* because the levels are all decreasing by `1` or `2`.
-    `1 2 7 8 9`: *Unsafe* because `2 7` is an increase of `5`.
-    `9 7 6 2 1`: *Unsafe* because `6 2` is a decrease of `4`.
-    `1 3 2 4 5`: *Unsafe* because `1 3` is increasing but `3 2` is decreasing.
-    `8 6 4 4 1`: *Unsafe* because `4 4` is neither an increase or a decrease.
-    `1 3 6 7 9`: *Safe* because the levels are all increasing by `1`, `2`, or `3`.
+- `7 6 4 2 1`: *Safe* because the levels are all decreasing by `1` or `2`.
+- `1 2 7 8 9`: *Unsafe* because `2 7` is an increase of `5`.
+- `9 7 6 2 1`: *Unsafe* because `6 2` is a decrease of `4`.
+- `1 3 2 4 5`: *Unsafe* because `1 3` is increasing but `3 2` is decreasing.
+- `8 6 4 4 1`: *Unsafe* because `4 4` is neither an increase or a decrease.
+- `1 3 6 7 9`: *Safe* because the levels are all increasing by `1`, `2`, or `3`.
 
 So, in this example, `2` reports are *safe*.
 
 Analyze the unusual data from the engineers. *How many reports are safe?*
 
 To begin, [get your puzzle input](input).
+
+Your puzzle answer was `472`.
+
+The first half of this puzzle is complete! It provides one gold star: *
+
+--- Part Two ---
+
+The engineers are surprised by the low number of safe reports until they realize they forgot to tell you about the Problem Dampener.
+
+The Problem Dampener is a reactor-mounted module that lets the reactor safety systems *tolerate a single bad level* in what would otherwise be a safe report. It's like the bad level never happened!
+
+Now, the same rules apply as before, except if removing a single level from an unsafe report would make it safe, the report instead counts as safe.
+
+More of the above example's reports are now safe:
+
+- `7 6 4 2 1`: `Safe` without removing any level.
+- `1 2 7 8 9`: `Unsafe` regardless of which level is removed.
+- `9 7 6 2 1`: `Unsafe` regardless of which level is removed.
+- `1 3 2 4 5`: `Safe` by removing the second level, `3`.
+- `8 6 4 4 1`: `Safe` by removing the third level, `4`.
+- `1 3 6 7 9`: `Safe` without removing any level.
+
+Thanks to the Problem Dampener, `4` reports are actually *safe*!
+
+Update your analysis by handling situations where the Problem Dampener can remove a single level from unsafe reports. *How many reports are now safe?*
+
+Answer: