Solution to problem 15 in Python

src/Year_2021/P15.py

@@ -0,0 +1,248 @@
+# --- Day 15: Chiton ---
+
+# You've almost reached the exit of the cave, but the walls are getting closer
+# together. Your submarine can barely still fit, though; the main problem is
+# that the walls of the cave are covered in chitons, and it would be best not to
+# bump any of them.
+
+# The cavern is large, but has a very low ceiling, restricting your motion to
+# two dimensions. The shape of the cavern resembles a square; a quick scan of
+# chiton density produces a map of risk level throughout the cave (your puzzle
+# input). For example:
+
+# 1163751742
+# 1381373672
+# 2136511328
+# 3694931569
+# 7463417111
+# 1319128137
+# 1359912421
+# 3125421639
+# 1293138521
+# 2311944581
+
+# You start in the top left position, your destination is the bottom right
+# position, and you cannot move diagonally. The number at each position is its
+# risk level; to determine the total risk of an entire path, add up the risk
+# levels of each position you enter (that is, don't count the risk level of your
+# starting position unless you enter it; leaving it adds no risk to your total).
+
+# Your goal is to find a path with the lowest total risk. In this example, a
+# path with the lowest total risk is highlighted here:
+
+# 1163751742
+# 1381373672
+# 2136511328
+# 3694931569
+# 7463417111
+# 1319128137
+# 1359912421
+# 3125421639
+# 1293138521
+# 2311944581
+
+# The total risk of this path is 40 (the starting position is never entered, so
+# its risk is not counted).
+
+# What is the lowest total risk of any path from the top left to the bottom
+# right?
+
+import heapq
+
+with open("files/P15.txt") as f:
+    grid = {
+        (x, y): int(n)
+        for y, row in enumerate(f.read().split("\n"))
+        for x, n in enumerate(row)
+    }
+    max_x, max_y = max(grid)
+
+
+def get_value(pos, width, height):
+    # Calculate additional components for the value
+    x_component = pos[0] // width
+    y_component = pos[1] // height
+
+    current_value = grid[pos[0] % width, pos[1] % height]
+    combined_value = current_value + x_component + y_component
+
+    if combined_value < 10:
+        return combined_value
+    else:
+        return combined_value % 9
+
+
+def bfs(width, height, scale):
+    queue, visited = [(0, 0, 0)], {(0, 0)}
+
+    while queue:
+        risk, x, y = heapq.heappop(queue)
+        # Check if we reached the target coordinates
+        if (x, y) == (width * scale - 1, height * scale - 1):
+            return risk
+
+        for neighb in ((x + 1, y), (x, y + 1), (x - 1, y), (x, y - 1)):
+            if neighb in visited:
+                continue
+            if (
+                0 <= neighb[0] < width * scale
+                and 0 <= neighb[1] < height * scale
+            ):
+                new_risk = risk + get_value(neighb, width, height)
+                visited.add(neighb)
+                heapq.heappush(queue, (new_risk, *neighb))
+
+
+def part1():
+    res = bfs(max_x + 1, max_y + 1, scale=1)
+    print(f"The lowest total risk is {res}")
+
+
+# --- Part Two ---
+
+# Now that you know how to find low-risk paths in the cave, you can try to find
+# your way out.
+
+# The entire cave is actually five times larger in both dimensions than you
+# thought; the area you originally scanned is just one tile in a 5x5 tile area
+# that forms the full map. Your original map tile repeats to the right and
+# downward; each time the tile repeats to the right or downward, all of its risk
+# levels are 1 higher than the tile immediately up or left of it. However, risk
+# levels above 9 wrap back around to 1. So, if your original map had some
+# position with a risk level of 8, then that same position on each of the 25
+# total tiles would be as follows:
+
+# 8 9 1 2 3
+# 9 1 2 3 4
+# 1 2 3 4 5
+# 2 3 4 5 6
+# 3 4 5 6 7
+
+# Each single digit above corresponds to the example position with a value of 8
+# on the top-left tile. Because the full map is actually five times larger in
+# both dimensions, that position appears a total of 25 times, once in each
+# duplicated tile, with the values shown above.
+
+# Here is the full five-times-as-large version of the first example above, with
+# the original map in the top left corner highlighted:
+
+# 11637517422274862853338597396444961841755517295286
+# 13813736722492484783351359589446246169155735727126
+# 21365113283247622439435873354154698446526571955763
+# 36949315694715142671582625378269373648937148475914
+# 74634171118574528222968563933317967414442817852555
+# 13191281372421239248353234135946434524615754563572
+# 13599124212461123532357223464346833457545794456865
+# 31254216394236532741534764385264587549637569865174
+# 12931385212314249632342535174345364628545647573965
+# 23119445813422155692453326671356443778246755488935
+# 22748628533385973964449618417555172952866628316397
+# 24924847833513595894462461691557357271266846838237
+# 32476224394358733541546984465265719557637682166874
+# 47151426715826253782693736489371484759148259586125
+# 85745282229685639333179674144428178525553928963666
+# 24212392483532341359464345246157545635726865674683
+# 24611235323572234643468334575457944568656815567976
+# 42365327415347643852645875496375698651748671976285
+# 23142496323425351743453646285456475739656758684176
+# 34221556924533266713564437782467554889357866599146
+# 33859739644496184175551729528666283163977739427418
+# 35135958944624616915573572712668468382377957949348
+# 43587335415469844652657195576376821668748793277985
+# 58262537826937364893714847591482595861259361697236
+# 96856393331796741444281785255539289636664139174777
+# 35323413594643452461575456357268656746837976785794
+# 35722346434683345754579445686568155679767926678187
+# 53476438526458754963756986517486719762859782187396
+# 34253517434536462854564757396567586841767869795287
+# 45332667135644377824675548893578665991468977611257
+# 44961841755517295286662831639777394274188841538529
+# 46246169155735727126684683823779579493488168151459
+# 54698446526571955763768216687487932779859814388196
+# 69373648937148475914825958612593616972361472718347
+# 17967414442817852555392896366641391747775241285888
+# 46434524615754563572686567468379767857948187896815
+# 46833457545794456865681556797679266781878137789298
+# 64587549637569865174867197628597821873961893298417
+# 45364628545647573965675868417678697952878971816398
+# 56443778246755488935786659914689776112579188722368
+# 55172952866628316397773942741888415385299952649631
+# 57357271266846838237795794934881681514599279262561
+# 65719557637682166874879327798598143881961925499217
+# 71484759148259586125936169723614727183472583829458
+# 28178525553928963666413917477752412858886352396999
+# 57545635726865674683797678579481878968159298917926
+# 57944568656815567976792667818781377892989248891319
+# 75698651748671976285978218739618932984172914319528
+# 56475739656758684176786979528789718163989182927419
+# 67554889357866599146897761125791887223681299833479
+
+# Equipped with the full map, you can now find a path from the top left corner
+# to the bottom right corner with the lowest total risk:
+
+# 11637517422274862853338597396444961841755517295286
+# 13813736722492484783351359589446246169155735727126
+# 21365113283247622439435873354154698446526571955763
+# 36949315694715142671582625378269373648937148475914
+# 74634171118574528222968563933317967414442817852555
+# 13191281372421239248353234135946434524615754563572
+# 13599124212461123532357223464346833457545794456865
+# 31254216394236532741534764385264587549637569865174
+# 12931385212314249632342535174345364628545647573965
+# 23119445813422155692453326671356443778246755488935
+# 22748628533385973964449618417555172952866628316397
+# 24924847833513595894462461691557357271266846838237
+# 32476224394358733541546984465265719557637682166874
+# 47151426715826253782693736489371484759148259586125
+# 85745282229685639333179674144428178525553928963666
+# 24212392483532341359464345246157545635726865674683
+# 24611235323572234643468334575457944568656815567976
+# 42365327415347643852645875496375698651748671976285
+# 23142496323425351743453646285456475739656758684176
+# 34221556924533266713564437782467554889357866599146
+# 33859739644496184175551729528666283163977739427418
+# 35135958944624616915573572712668468382377957949348
+# 43587335415469844652657195576376821668748793277985
+# 58262537826937364893714847591482595861259361697236
+# 96856393331796741444281785255539289636664139174777
+# 35323413594643452461575456357268656746837976785794
+# 35722346434683345754579445686568155679767926678187
+# 53476438526458754963756986517486719762859782187396
+# 34253517434536462854564757396567586841767869795287
+# 45332667135644377824675548893578665991468977611257
+# 44961841755517295286662831639777394274188841538529
+# 46246169155735727126684683823779579493488168151459
+# 54698446526571955763768216687487932779859814388196
+# 69373648937148475914825958612593616972361472718347
+# 17967414442817852555392896366641391747775241285888
+# 46434524615754563572686567468379767857948187896815
+# 46833457545794456865681556797679266781878137789298
+# 64587549637569865174867197628597821873961893298417
+# 45364628545647573965675868417678697952878971816398
+# 56443778246755488935786659914689776112579188722368
+# 55172952866628316397773942741888415385299952649631
+# 57357271266846838237795794934881681514599279262561
+# 65719557637682166874879327798598143881961925499217
+# 71484759148259586125936169723614727183472583829458
+# 28178525553928963666413917477752412858886352396999
+# 57545635726865674683797678579481878968159298917926
+# 57944568656815567976792667818781377892989248891319
+# 75698651748671976285978218739618932984172914319528
+# 56475739656758684176786979528789718163989182927419
+# 67554889357866599146897761125791887223681299833479
+
+# The total risk of this path is 315 (the starting position is still never
+# entered, so its risk is not counted).
+
+# Using the full map, what is the lowest total risk of any path from the top
+# left to the bottom right?
+
+
+def part2():
+    res = bfs(max_x + 1, max_y + 1, 5)
+    print(f"The lowest total risk is {res}")
+
+
+if __name__ == "__main__":
+    part1()
+    part2()

src/Year_2021/files/P15.txt

@@ -0,0 +1,100 @@
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