Merge branch 'master' of github.com:failedxyz/easyctf

library/generator.py

@@ -0,0 +1,11 @@
+import random
+C = input()
+
+if C==1:
+  print 1
+elif C==2:
+  print 2
+elif C==3 or C==4:
+  print random.randint(3, 100)
+else:
+  print random.randint(2**(C**3-1), 2**(C**3))

library/grader.py

@@ -0,0 +1,39 @@
+x = input() + 1
+
+mat = [[0,0,1,0],[0,1,0,1],[1,0,2,0],[0,2,0,1]]
+mod = 10**9+7
+
+def egcd(a, b):
+    if a == 0:
+        return (b, 0, 1)
+    else:
+        g, y, x = egcd(b % a, a)
+        return (g, x - (b // a) * y, y)
+
+def modinv(a, m):
+    g, x, y = egcd(a, m)
+    if g != 1:
+        raise Exception('modular inverse does not exist')
+    else:
+        return x % m
+
+def matmult(mtx_a, mtx_b, mod):
+    tpos_b = zip( *mtx_b)
+    rtn = [[ sum( ea*eb for ea,eb in zip(a,b))%mod for b in tpos_b] for a in mtx_a]
+    return rtn
+
+def trace(A):
+    return sum(A[j][j] for j in range(len(A)))
+
+def matpow(A, p):
+    ret = A
+    for bit in bin(p)[3:]:
+        ret = matmult(ret, ret, mod)
+        if bit=='1':
+            ret = matmult(ret, A, mod)
+    return ret
+
+inv4 = modinv(4, mod)
+ans = trace(matpow(mat, x))%mod
+ans = (ans * inv4)% mod
+print ans

library2/description.md

@@ -28,3 +28,7 @@ Output:
 ```
 1
 ```
+
+Explanation: 
+
+If you understand the word 'ok', you can understand the word 'blah'. If you understand 'ok' and 'blah', you can understand 'iz'. 'iz', and 'ok' lets you understand 'yiq'. 'yiq', 'iz', and 'blah' let you understand 'arggiq'.