sudoku

y2020/p99.py

@@ -0,0 +1,47 @@
+import re
+import sys
+
+
+def solve_sudoku(string):
+    known = [(i, v) for i, v in enumerate(string) if v != '0']
+    solved, = map(dict, solve(X, Y, known))
+    return ''.join(solved[i] for i in range(81))
+
+
+def solve(X, Y, solution):
+    for choice in solution:
+        X = select(X, Y, choice)
+
+    for solution in complete(X, Y, solution):
+        yield solution
+
+
+def select(X, Y, choice):
+    fulfilled = Y[choice]
+    excluded = {y for x in fulfilled for y in X[x]}
+    return {x: ys - excluded for x, ys in X.items() if x not in fulfilled}
+
+
+def complete(X, Y, solution):
+    if not X:
+        yield solution
+    else:
+        for choice in min(X.values(), key=len):
+            yield from complete(select(X, Y, choice), Y, solution + [choice])
+
+
+Y, X = {}, {}
+for i in range(81):
+    r = i // 9
+    c = i % 9
+    b = r // 3 * 3 + c // 3
+    for v in '123456789':
+        choice = (i, v)
+        Y[choice] = {('p', i), ('r', r, v), ('c', c, v), ('b', b, v)}
+        for x in Y[choice]:
+            X.setdefault(x, set()).add(choice)
+
+
+text = sys.stdin.read()
+strings = re.split(r'Grid \d\d', text.replace('\n', ''))[1:]
+print(sum(int(solve_sudoku(string)[:3]) for string in strings))