재밌는 계단수들

zeta_python/completed/18244.py

@@ -0,0 +1,23 @@
+N = int(input())
+
+Mem = [[[-1] * 5 for _ in range(0, 10)] for _ in range(N)]
+
+
+def I(l, k, b):
+    if b > 2 or b < -2:
+        return 0
+    if l == 0:
+        return 1
+    if Mem[l - 1][k][b] != -1:
+        return Mem[l - 1][k][b]
+
+    re = 0
+    if 0 < k:
+        re += I(l - 1, k - 1, b - 1 if b < 0 else -1) % 1000000007
+    if k < 9:
+        re += I(l - 1, k + 1, b + 1 if b > 0 else 1) % 1000000007
+    Mem[l - 1][k][b] = re
+    return re
+
+
+print(sum(I(N - 1, i, 0) for i in range(0, 10)) % 1000000007)