nth_ele add testcase

Author: PegasusWang

docs/13_高级排序算法/quick_sort.md

@@ -128,5 +128,5 @@ T(n) = 2T(n/2) + n
 
 # Leetcode
 
-无序数组寻找第 k 大的数字。
+无序数组寻找第 k 大的数字，不止一种方法。
 https://leetcode.com/problems/kth-largest-element-in-an-array/description/

docs/13_高级排序算法/quicksort.py

@@ -102,6 +102,9 @@ def test_nth_element():
     assert nth_element(array, 0, len(array), 1) == 1
     assert nth_element(array, 0, len(array), 2) == 2
 
+    array = [3,3,3,3,3,3,3,3,3]
+    assert nth_element(array, 0, len(array), 1) == 3
+
 
 if __name__ == '__main__':
     test_nth_element()