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y2019/p22.py

@@ -0,0 +1,22 @@
+import sys
+
+
+def shuffle(text, L, P):
+    cards = list(range(L))
+    for line in text.splitlines():
+        inst, n = line.rsplit(' ', 1)
+        if inst == 'deal with increment':
+            n = int(n)
+            invmod = pow(n, -1, L)  # pow(n, L - 2, L)
+            source = lambda i: i * invmod % L  # noqa
+        elif inst == 'cut':
+            n = int(n)
+            source = lambda i: (i + n) % L  # noqa
+        elif inst == 'deal into new':
+            source = lambda i: (L - 1 - i) % L  # noqa
+        cards = [cards[source(i)] for i in range(L)]
+    return cards.index(P)
+
+
+text = sys.stdin.read()
+print(shuffle(text, 10007, 2019))