From ed2e4f1403eff3c48df2576b46d2116f64f3fcfa Mon Sep 17 00:00:00 2001
From: Lachlan Meyer <lachlanmeyer@gmail.com>
Date: Fri, 20 Dec 2024 20:01:15 +1100
Subject: [PATCH] 20-2 - slow - might need numpy for better performance

---
 2024/20/20-2.py | 64 +++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 64 insertions(+)
 create mode 100644 2024/20/20-2.py

diff --git a/2024/20/20-2.py b/2024/20/20-2.py
new file mode 100644
index 0000000..f9f8324
--- /dev/null
+++ b/2024/20/20-2.py
@@ -0,0 +1,64 @@
+import networkx as nx
+
+map = set()
+directions = [(1, 0), (0, 1), (-1, 0), (0, -1)]
+
+testing = False
+
+minimumStepsSaved = 50 if testing else 100
+picosecondsCheatable = 20
+totalGoodCheats = 0
+
+filename = 'testinput' if testing else 'input'
+
+with open(f'2024/20/{filename}.txt') as f:
+    g = nx.DiGraph()
+    for j, line in enumerate(f):
+        line = line.strip()
+        for i, char in enumerate(line):
+            if char == '#':
+                continue
+            if char == 'E':
+                e = (i, j)
+            if char == 'S':
+                s = (i, j) # reindeer starts pointing west
+
+            map.add((i,j))
+            
+for node in map:
+    x, y = node
+    for direction in directions:
+        dirX, dirY = direction
+        neighbour = (x + dirX, y + dirY)
+        
+        if neighbour in map: 
+            g.add_edge(node, neighbour, weight=1)
+
+
+shortestPath = nx.shortest_path(g, s, e, weight='weight')
+
+
+def getCheatEndpoints(coords):
+    i, j = coords
+    output = set()
+    for distanceX in range(-picosecondsCheatable, picosecondsCheatable + 1):
+        distanceYMax = picosecondsCheatable - abs(distanceX)
+        for distanceY in range(-distanceYMax, distanceYMax + 1):
+            if (i + distanceX, j + distanceY) in shortestPath:
+                output.add((i + distanceX, j + distanceY))
+    return output
+
+for i, node in enumerate(shortestPath):
+    potentialCheatNodes = getCheatEndpoints(node)
+    for potentialCheat in potentialCheatNodes:
+        j = shortestPath.index(potentialCheat)
+
+        manhattanDistance = abs(node[0] - potentialCheat[0]) + abs(node[1] - potentialCheat[1])
+
+        stepsSaved = j - i - manhattanDistance
+        if stepsSaved < minimumStepsSaved:
+            continue 
+
+        totalGoodCheats += 1
+
+print(totalGoodCheats)
\ No newline at end of file