Solution to problem 1 in Python

src/Year_2019/P1.py

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+# --- Day 1: The Tyranny of the Rocket Equation ---
+
+# Santa has become stranded at the edge of the Solar System while delivering
+# presents to other planets! To accurately calculate his position in space,
+# safely align his warp drive, and return to Earth in time to save Christmas,
+# he needs you to bring him measurements from fifty stars.
+
+# Collect stars by solving puzzles. Two puzzles will be made available on each
+# day in the Advent calendar; the second puzzle is unlocked when you complete
+# the first. Each puzzle grants one star. Good luck!
+
+# The Elves quickly load you into a spacecraft and prepare to launch.
+
+# At the first Go / No Go poll, every Elf is Go until the Fuel Counter-Upper.
+# They haven't determined the amount of fuel required yet.
+
+# Fuel required to launch a given module is based on its mass. Specifically, to
+# find the fuel required for a module, take its mass, divide by three, round
+# down, and subtract 2.
+
+# For example:
+
+#     For a mass of 12, divide by 3 and round down to get 4, then subtract 2 to
+# get 2.
+#     For a mass of 14, dividing by 3 and rounding down still yields 4, so the
+# fuel required is also 2.
+#     For a mass of 1969, the fuel required is 654.
+#     For a mass of 100756, the fuel required is 33583.
+
+# The Fuel Counter-Upper needs to know the total fuel requirement. To find it,
+# individually calculate the fuel needed for the mass of each module (your
+# puzzle input), then add together all the fuel values.
+
+# What is the sum of the fuel requirements for all of the modules on your
+# spacecraft?
+
+with open("files/P1.txt") as f:
+    fuel = [int(line) for line in f.read().strip().split()]
+
+# fuel = [12, 14, 1969, 100756]
+
+
+def part_1() -> None:
+    requirements = []
+    for mass in fuel:
+        # integer division
+        fuel_required = round(mass // 3) - 2
+        requirements.append(fuel_required)
+
+    print(f"The sum of fuel requirement is {sum(requirements)}")
+
+
+# --- Part Two ---
+
+# During the second Go / No Go poll, the Elf in charge of the Rocket Equation
+# Double-Checker stops the launch sequence. Apparently, you forgot to include
+# additional fuel for the fuel you just added.
+
+# Fuel itself requires fuel just like a module - take its mass, divide by
+# three, round down, and subtract 2. However, that fuel also requires fuel, and
+# that fuel requires fuel, and so on. Any mass that would require negative fuel
+# should instead be treated as if it requires zero fuel; the remaining mass, if
+# any, is instead handled by wishing really hard, which has no mass and is
+# outside the scope of this calculation.
+
+# So, for each module mass, calculate its fuel and add it to the total. Then,
+# treat the fuel amount you just calculated as the input mass and repeat the
+# process, continuing until a fuel requirement is zero or negative. For
+# example:
+
+#     A module of mass 14 requires 2 fuel. This fuel requires no further fuel
+# (2 divided by 3 and rounded down is 0, which would call for a negative fuel),
+# so the total fuel required is still just 2.
+#     At first, a module of mass 1969 requires 654 fuel. Then, this fuel
+# requires 216 more fuel (654 / 3 - 2). 216 then requires 70 more fuel, which
+# requires 21 fuel, which requires 5 fuel, which requires no further fuel. So,
+# the total fuel required for a module of mass 1969 is 654 + 216 + 70 + 21 + 5
+# = 966.
+#     The fuel required by a module of mass 100756 and its fuel is:
+# 33583 + 11192 + 3728 + 1240 + 411 + 135 + 43 + 12 + 2 = 50346.
+
+# What is the sum of the fuel requirements for all of the modules on your
+# spacecraft when also taking into account the mass of the added fuel?
+# (Calculate the fuel requirements for each module separately, then add them
+# all up at the end.)
+
+
+def part_2() -> None:
+    requirements = []
+    for mass in fuel:
+        # integer division
+        fuel_required = round(mass // 3) - 2
+        requirements.append(fuel_required)
+        # keep going until zero or negative
+        while fuel_required > 0:
+            fuel_required = round(fuel_required // 3) - 2
+            # if negative, do not add
+            if fuel_required > 0:
+                requirements.append(fuel_required)
+
+    print(f"The sum of the new fuel requirement is {sum(requirements)}")
+
+
+if __name__ == "__main__":
+    part_1()
+    part_2()