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

Counting sort python

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)