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diff --git a/heapsort.py b/heapsort.py
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+++ b/heapsort.py
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+# Copyright 2015 Egor Tensin <Egor.Tensin@gmail.com>
+# This file is licensed under the terms of the MIT License.
+# See LICENSE.txt for details.
+
+# Disclaimer: implemented in the most literate way.
+
+def heapsort(xs):
+    heapify(xs)
+    first, last = 0, len(xs) - 1
+    for end in range(last, first, -1):
+        xs[end], xs[first] = xs[first], xs[end]
+        siftdown(xs, first, end - 1)
+    return xs
+
+# In a heap stored in a zero-based array,
+# left_child = node * 2 + 1
+# right_child = node * 2 + 2
+# parent = (node - 1) // 2
+
+def _get_parent(node):
+    return (node - 1) // 2
+
+def _get_left_child(node):
+    return node * 2 + 1
+
+def _get_right_child(node):
+    return node * 2 + 2
+
+def heapify(xs):
+    last = len(xs) - 1
+    first_parent, last_parent = 0, _get_parent(last)
+    for parent in range(last_parent, first_parent - 1, -1):
+        siftdown(xs, parent, last)
+
+def siftdown(xs, start, end):
+    root = start
+    while True:
+        # We swap if there is at least one child
+        child = _get_left_child(root)
+        if child > end:
+            break
+        # If there are two children, select the minimum
+        right_child = _get_right_child(root)
+        if right_child <= end and xs[child] < xs[right_child]:
+            child = right_child
+        if xs[root] < xs[child]:
+            xs[root], xs[child] = xs[child], xs[root]
+            root = child
+        else:
+            break
+
+if __name__ == '__main__':
+    import sys
+    print(heapsort(list(map(int, sys.argv[1:]))))