day 10 optimizations

- reduce duplicate queue entries by not appending to the queue if a
  point has a nonzero count. (if there's a count then it must have
  already been queued.)

- use the correct data structure for a double-ended queue so pop(0) has
  less work to do

- factor out the list of summits

of these three changes, only the last one has any noticable effect
on the run time. 🤷

day10/input

@@ -0,0 +1,58 @@
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day10/sample5.in

@@ -0,0 +1,8 @@
+89010123
+78121874
+87430965
+96549874
+45678903
+32019012
+01329801
+10456732

day10/sol.py

@@ -0,0 +1,58 @@
+import itertools 
+from collections import Counter, deque
+def read(file):
+    return [line.strip() for line in file]
+
+def solve(file):
+    grid = read(file)
+    ny = len(grid)
+    nx = len(grid[0])
+    points = lambda: itertools.product(range(nx), range(ny))
+
+    def get(x,y):
+        if 0 <= x < nx and 0 <= y < ny:
+            return grid[y][x]
+        return '.'
+
+    def visit(x,y,h,n):
+        c = get(x,y)
+        if c == h:
+            assert (x,y) not in done
+            if (x,y) not in count:
+                queue.append((x,y))
+            count[x,y] += n
+
+    trailheads = [(x,y) for x,y in points() if get(x,y) == '0']
+    summits = [(x,y) for x,y in points() if get(x,y) == '9']
+
+    t1 = 0
+    t2 = 0
+    for p in trailheads:
+        queue = deque([p])
+        done = set()
+        count = Counter()
+        count[p] = 1
+        while queue:
+            x,y = queue.popleft()
+            #print(x,y,queue)
+            if (x,y) in done:
+                continue
+            done.add((x,y))
+            n = count[x,y]
+            c = get(x,y)
+            if c != '.' and c != '9':
+                h = str(int(c)+1)
+                visit(x+1,y,h,n)
+                visit(x-1,y,h,n)
+                visit(x,y+1,h,n)
+                visit(x,y-1,h,n)
+        for x,y in summits:
+            if (x,y) in done:
+                t1 += 1
+                t2 += count[x,y]
+                
+    print(t1)
+    print(t2)
+
+solve(open("sample5.in"))
+solve(open("input"))