add partition testcase

Author: PegasusWang

docs/13_高级排序算法/quick_sort.md

@@ -128,4 +128,5 @@ T(n) = 2T(n/2) + n
 
 # Leetcode
 
+无序数组寻找第 k 大的数字。
 https://leetcode.com/problems/kth-largest-element-in-an-array/description/

docs/13_高级排序算法/quicksort.py

@@ -57,6 +57,10 @@ def test_partition():
     assert partition(l, 0, len(l)) == 0
     l = [4, 3, 2, 1]
     assert partition(l, 0, len(l)) == 3
+    l = [1]
+    assert partition(l, 0, len(l)) == 0
+    l = [2,1]
+    assert partition(l, 0, len(l)) == 1
 
 
 def test_quicksort_inplace():
@@ -91,6 +95,9 @@ def test_nth_element():
     for i in reversed(l):
         assert nth_element(l, 0, len(l), i) == i
 
+    array = [3, 2, 1, 5, 6, 4]
+    assert nth_element(array, 0, len(array), 2) == 2
+
 
 if __name__ == '__main__':
     test_nth_element()