Merge pull request #5 from PoApper/feat/bino

New exercise for recursion: Binomial Coefficient

Author: sohnryang

04-functions-modules/binomial_coeff-answer.py

@@ -0,0 +1,25 @@
+def binomial_coefficient(n, k):
+    """
+    Calcaulate binomial coefficient nCk, using recursion.
+    Hint:
+    nCk = (n - 1)C(k - 1) + (n - 1)Ck
+    nC0 = 1
+
+    >>> binomial_coefficient(1, 0)
+    1
+    >>> binomial_coefficient(4, 2)
+    6
+    >>> binomial_coefficient(4, 3)
+    4
+    """
+    if k == 0:
+        return 1
+    elif n <= 0 or k < 0:
+        return 0
+    return binomial_coefficient(n - 1, k - 1) + binomial_coefficient(n - 1, k)
+
+
+if __name__ == "__main__":
+    import doctest
+
+    doctest.testmod(verbose=True)

04-functions-modules/binomial_coeff.py

@@ -0,0 +1,21 @@
+def binomial_coefficient(n, k):
+    """
+    Calcaulate binomial coefficient nCk, using recursion.
+    Hint:
+    nCk = (n - 1)C(k - 1) + (n - 1)Ck
+    nC0 = 1
+
+    >>> binomial_coefficient(1, 0)
+    1
+    >>> binomial_coefficient(4, 2)
+    6
+    >>> binomial_coefficient(4, 3)
+    4
+    """
+    pass
+
+
+if __name__ == "__main__":
+    import doctest
+
+    doctest.testmod(verbose=True)

04-functions-modules/guide.md

@@ -6,3 +6,11 @@
 - background: list, iteration
 
 Implement `min`, `max` functions on your own.
+
+## Binomial Coefficient
+
+- difficulty: ★★☆
+- time: ~ 30m for beginners
+- background: function, recursion
+
+Implement a function which calculates binomial coefficient, $\prescript{}{n}C_k$.