From ab31f1a3a89fbc49c3bf77866d626c4afc653b9e Mon Sep 17 00:00:00 2001
From: Isidro Arias <isidroariass@hotmail.es>
Date: Fri, 18 Apr 2025 10:11:28 +0200
Subject: [PATCH] Add median() function using Quickselect
---
searches/quick_select.py | 31 +++++++++++++++++++++++++++++++
1 file changed, 31 insertions(+)
diff --git a/searches/quick_select.py b/searches/quick_select.py
index c8282e1fa5fc..6236074ffc54 100644
--- a/searches/quick_select.py
+++ b/searches/quick_select.py
@@ -60,3 +60,34 @@ def quick_select(items: list, index: int):
# must be in larger
else:
return quick_select(larger, index - (m + count))
+
+
+def median(data: list):
+ """One common application of Quickselect is finding the median, which is
+ the middle element (or average of the two middle elements) in a dataset. It
+ works efficiently on unsorted lists by partially sorting the data without
+ fully sorting the entire list.
+
+ >>> import random
+ >>> random.seed(0)
+
+ >>> d = [2, 2, 3, 9, 9]
+ >>> random.shuffle(d)
+ >>> d
+ [3, 2, 2, 9, 9]
+ >>> median(d)
+ 3
+
+ >>> d = [2, 2, 3, 9, 9, 9]
+ >>> random.shuffle(d)
+ >>> median(d)
+ 6.0
+
+ """
+ mid, rest = divmod(len(data), 2)
+ if rest:
+ return quick_select(data, mid)
+ else:
+ low_mid = quick_select(data, mid - 1)
+ high_mid = quick_select(data, mid)
+ return (low_mid + high_mid) / 2