Solve problem 122.

python/e122.py

@@ -0,0 +1,27 @@
+def euler_122():
+    upper = 201
+    m_k = {k: 0 for k in range(2, upper)}
+    sets = [[1]]
+    for _ in range(11):
+        new_sets = []
+        for s in sets:
+            for i in range(len(s)):
+                new_elem = s[i] + s[-1]
+                if new_elem in m_k and m_k[new_elem] == 0:
+                    m_k[new_elem] = len(s)
+                new_sets.append(s + [new_elem])
+
+        # For better performance, we would have to prune here.
+        sets = new_sets
+
+    r = 0
+    for k in range(2, upper):
+        assert m_k[k] != 0
+        r += m_k[k]
+    return r
+
+
+if __name__ == "__main__":
+    solution = euler_122()
+    print("e122.py: " + str(solution))
+    assert solution == 1582