day 6: almost there for part 2 but no

d06/part2.py

@@ -0,0 +1,114 @@
+import sys, os
+from collections import Counter as C
+from collections import defaultdict as dd
+
+"""
+same convention as SVG
+           W
+(0,0)┌───────────► x
+     │                
+  H  │                
+     │                
+     │                
+     ▼                
+     y
+grid G store list of rows
+to get G(x,y), must first extract row y and then col y => G[y][x]
+"""
+
+def grid_geom(G):
+    H = len(G)
+    W = len(G[0])
+    return W, H
+
+def in_grid(G, x, y) -> bool:
+    W, H = grid_geom(G)
+    return x>=0 and x<W and y>=0 and y<H
+
+def get_in_grid(G, x, y):
+    if in_grid(W, H, x,y):
+        return G[y][x]
+
+UP = (0,-1) ; RIGHT = (1,0) ; DOWN = (0,1) ; LEFT = (-1,0)
+M4=[ UP, RIGHT, DOWN, LEFT ]
+D4 = [(1,1),(-1,-1),(1,-1),(-1,1)]
+M8 = M4 + D4
+
+L = sys.stdin.read().strip().split("\n")
+G = [list(l) for l in L]
+
+W, H = grid_geom(G)
+
+# 1: find guard
+gx = gy = 0
+for i in range(H):  # rows
+    for j in range(W):  # cols
+        if G[i][j] == '^':
+            gx = j
+            gy = i
+
+# 2: compute guard's walk
+M4N = { M4[i-1]:M4[i] for i in range(len(M4))}
+print(f'{M4N=}')
+S = 0
+V = C()  # visited
+T = dd(set)  # each position forcing a turn, grouped by turn type
+sens = M4[0]
+on = True
+while on : # in the map
+    V[(gx,gy)] +=1
+    (dx,dy) = sens
+    gxn = gx + dx
+    gyn = gy + dy
+    #print(S, sens, dx, dy, gxn, gyn)
+    if not in_grid(G, gxn, gyn): # off the map
+        on = False
+    elif G[gyn][gxn] == '#':  # must turn
+        T[sens].add((gxn,gyn))
+        sens = M4N[sens]
+    else:  # move
+        gx = gxn
+        gy = gyn
+        S += 1
+print(S, len(V))
+
+for (x,y) in V.keys():
+    G[y][x] = "o"
+for row in G:
+    #print(" ".join(row))
+    pass
+
+M = 0
+for m, v in T.items():
+    (dx,dy) = m
+    for (x,y) in v:
+        print(f"{dx},{dy}:for", (x,y))
+        # find a position for nearest next turn
+        n = None
+        (dxn, dyn) = M4N[m]
+        for i in range(1,10):
+            cn = (x-dx+i*dxn,y-dy+i*dyn)
+            #print(f'{cn=}')
+            if cn in T[M4N[m]]:
+                n = cn
+                print("  found n", n)
+                break
+        if n:
+            (xn,yn) = n
+            (dxp, dyp) = M4N[M4N[m]]
+            p = None
+            print(f"    lookfor p {dxp=},{dyp=}")
+            for i in range(1,10):
+                cp = (xn-dxn+i*dxp,yn-dyn+i*dyp)
+                #print(f'{cp=}')
+                if cp in T[M4N[M4N[m]]]:
+                    p = cp
+                    print("    found p", p)
+                    break
+            if p:
+                print((x,y),n,p)
+                M+=1
+   # break
+print(M)
+            
+