Day 7

Author: Vic-Nas

aoc/2025/07/normal/07_normal.vn.py

@@ -1,4 +1,68 @@
 # Advent of code Day 07
 # https://adventofcode.com/2025/day/7
 # 07/12/2025
-    
+
+
+with open("input.txt") as file:
+    inp = list(map(
+        lambda s: list(s.strip()), 
+        file.readlines()
+    ))
+    
+
+res1, res2 = 0, 1
+
+from copy import deepcopy
+rows = deepcopy(inp)
+
+for i, row in enumerate(rows[:-2]):
+    if i % 2 == 1: continue
+    for j, el in enumerate(row):
+        if el in ["^", "."]: continue
+        down = rows[i + 2][j]
+        if down != "^":
+            rows[i + 2][j] = "|"
+        else:
+            res1 += 1
+            if j - 1 >= 0:
+                rows[i + 2][j - 1] = "|"
+
+            if j + 1 < len(row):
+                rows[i + 2][j + 1] = "|"
+
+
+nRows = len(inp)
+nCols = len(inp[0])
+
+# dp[i][j] = number of ways to reach position (i, j)
+dp = [[0] * nCols for _ in range(nRows)]
+
+
+startCol = inp[0].index("S")
+dp[0][startCol] = 1  # 1 way to start
+
+for i in range(0, nRows - 2, 2):
+    for j in range(nCols):
+        if dp[i][j] == 0:  # No way to get here
+            continue
+        
+        cpt = dp[i][j]  # Number of ways to get here
+        downRow = i + 2
+        down = inp[downRow][j]
+        
+        if down != "^":
+            # Just falls
+            dp[downRow][j] += cpt
+        else:
+            # Can go left or right
+            if j > 0 and inp[downRow][j - 1] != "|":
+                dp[downRow][j - 1] += cpt
+            
+            if j + 1 < nCols and inp[downRow][j + 1] != "|":
+                dp[downRow][j + 1] += cpt
+
+# Sum all positions in the last row
+lastRow = nRows - 2
+res2 = sum(dp[lastRow])
+
+print(res1, res2)