added function for Python3 (#1)

Author: kgashok

recipes/Python/Combination without using factorials/combo.py

@@ -7,3 +7,10 @@ def ncr(n, r):
     num     = reduce(op.mul, xrange(n, n-1, -1))
     denom   = reduce(op.mul, xrange(1, r+1))
     return num // denom
+
+def ncr3(n, r):
+    r       = min(r, n-r)
+    if x == 0: return 1
+    num     = reduce(op.mul, range(n, n-1, -1))
+    denom   = reduce(op.mul, range(1, r+1))
+    return num // denom