Added solution to problem 31

problem31.py

+#!/usr/bin/env python
+def pos(amt, coins):
+    p = 0
+
+    for i, c in enumerate(coins):
+        if c == amt:
+            p += 1
+        elif c < amt:
+            p += pos(amt - c, coins[i:])
+
+    return p
+
+print pos(200, [1, 2, 5, 10, 20, 50, 100, 200])