Move to proper folder

src/Year_2022/Day12.py

@@ -0,0 +1,140 @@
+# --- Day 12: Hill Climbing Algorithm ---
+
+# You try contacting the Elves using your handheld device, but the river you're
+# following must be too low to get a decent signal.
+
+# You ask the device for a heightmap of the surrounding area (your puzzle
+# input). The heightmap shows the local area from above broken into a grid;
+# the elevation of each square of the grid is given by a single lowercase
+# letter, where a is the lowest elevation, b is the next-lowest, and so on up
+# to the highest elevation, z.
+
+# Also included on the heightmap are marks for your current position (S) and
+# the location that should get the best signal (E). Your current position (S)
+# has elevation a, and the location that should get the best signal (E) has
+# elevation z.
+
+# You'd like to reach E, but to save energy, you should do it in as few steps
+# as possible. During each step, you can move exactly one square up, down,
+# left, or right. To avoid needing to get out your climbing gear, the elevation
+# of the destination square can be at most one higher than the elevation of
+# your current square; that is, if your current elevation is m, you could step
+# to elevation n, but not to elevation o. (This also means that the elevation
+# of the destination square can be much lower than the elevation of your
+# current square.)
+
+# For example:
+
+# Sabqponm
+# abcryxxl
+# accszExk
+# acctuvwj
+# abdefghi
+
+# Here, you start in the top-left corner; your goal is near the middle. You
+# could start by moving down or right, but eventually you'll need to head
+# toward the e at the bottom. From there, you can spiral around to the goal:
+
+# v..v<<<<
+# >v.vv<<^
+# .>vv>E^^
+# ..v>>>^^
+# ..>>>>>^
+
+# In the above diagram, the symbols indicate whether the path exits each
+# square moving up (^), down (v), left (<), or right (>). The location that
+# should get the best signal is still E, and . marks unvisited squares.
+
+# This path reaches the goal in 31 steps, the fewest possible.
+
+# What is the fewest steps required to move from your current position to the
+# location that should get the best signal?
+
+with open("/home/xfeluser/AoC_2022/P12.txt") as f:
+    diagram = {
+        (x, y): ord(e)
+        for y, line in enumerate(f.read().strip().split("\n"))
+        for x, e in enumerate(line.strip())
+    }
+
+start = [k for k in diagram if diagram[k] == ord("S")][0]
+end = [k for k in diagram if diagram[k] == ord("E")][0]
+# Use expected value for starting/ending point
+diagram[start] = ord("a")
+diagram[end] = ord("z")
+
+queue = [(start, 0)]
+pos_to_steps = {}
+
+while queue:
+    cur, steps = queue.pop()
+
+    if cur not in pos_to_steps or steps < pos_to_steps[cur]:
+        pos_to_steps[cur] = steps
+
+        for offset in ((1, 0), (-1, 0), (0, 1), (0, -1)):
+            new_pos = cur[0] + offset[0], cur[1] + offset[1]
+
+            if new_pos in diagram and diagram[new_pos] - diagram[cur] <= 1:
+                queue.append((new_pos, steps + 1))
+
+print(pos_to_steps[end])
+
+
+# --- Part Two ---
+
+# As you walk up the hill, you suspect that the Elves will want to turn this
+# into a hiking trail. The beginning isn't very scenic, though; perhaps you can
+# find a better starting point.
+
+# To maximize exercise while hiking, the trail should start as low as possible:
+# elevation a. The goal is still the square marked E. However, the trail should
+# still be direct, taking the fewest steps to reach its goal. So, you'll need
+# to find the shortest path from any square at elevation a to the square marked
+# E.
+
+# Again consider the example from above:
+
+# Sabqponm
+# abcryxxl
+# accszExk
+# acctuvwj
+# abdefghi
+
+# Now, there are six choices for starting position (five marked a, plus the
+# square marked S that counts as being at elevation a). If you start at the
+# bottom-left square, you can reach the goal most quickly:
+
+# ...v<<<<
+# ...vv<<^
+# ...v>E^^
+# .>v>>>^^
+# >^>>>>>^
+
+# This path reaches the goal in only 29 steps, the fewest possible.
+
+# What is the fewest steps required to move starting from any square with
+# elevation a to the location that should get the best signal?
+
+starts = []
+pos_to_steps = {}
+
+for start in [k for k in diagram if diagram[k] == ord("a")]:
+    queue = [(start, 0)]
+
+    while queue:
+        cur, steps = queue.pop()
+
+        if cur not in pos_to_steps or steps < pos_to_steps[cur]:
+            pos_to_steps[cur] = steps
+
+            for offset in ((1, 0), (-1, 0), (0, 1), (0, -1)):
+                new_pos = cur[0] + offset[0], cur[1] + offset[1]
+
+                if new_pos in diagram and diagram[new_pos] - diagram[cur] <= 1:
+                    queue.append((new_pos, steps + 1))
+
+    if end in pos_to_steps:
+        starts.append(pos_to_steps[end])
+
+print(min(starts))