Merge pull request wangzheng0822#87 from jerryderry/counting-sort-python

Counting sort python

Author: wangzheng0822

python/14_sorts/counting_sort.py

@@ -0,0 +1,40 @@
+"""
+ 计数排序
+
+ Author: Wenru
+"""
+
+from typing import List
+import itertools
+
+def counting_sort(a: List[int]):
+ if len(a) <= 1: return
+ 
+ # a中有counts[i]个数不大于i
+ counts = [0] * (max(a) + 1)
+ for num in a:
+ counts[num] += 1
+ counts = list(itertools.accumulate(counts))
+
+ # 临时数组，储存排序之后的结果
+ a_sorted = [0] * len(a)
+ for num in reversed(a):
+ index = counts[num] - 1
+ a_sorted[index] = num
+ counts[num] -= 1
+ 
+ a = a_sorted
+
+
+if __name__ == "__main__":
+ a1 = [1, 2, 3, 4]
+ counting_sort(a1)
+ print(a1)
+
+ a2 = [1, 1, 1, 1]
+ counting_sort(a2)
+ print(a2)
+
+ a3 = [4, 5, 0, 9, 3, 3, 1, 9, 8, 7]
+ counting_sort(a3)
+ print(a3)