sorts: Add insertion sort

sorts/src/insertion_sort.rs

@@ -0,0 +1,31 @@
+// Copyright (c) 2023 Xu Shaohua <[email protected]>. All rights reserved.
+// Use of this source is governed by General Public License that can be
+// found in the LICENSE file.
+
+/// Place one element at a time, inserting each into its proper place.
+///
+/// The elements to the left of the current index are in sorted order during
+/// the sort, but they are not in their final positions, as they may have to
+/// be moved to make room for smaller elements later.
+///
+/// 其思路是, 先将前 i 个元素调整为增序的, 随着 i 从 0 增大到 n, 整个序列
+/// 就变得是增序了.
+///
+/// 如果传数的数据是增序排好的, 那么只需要 N-1 次的比较, 以及 0 次的交换;
+/// 如果传数的数据是降序排好的, 那么需要 N^2/2 次的比较, 以及 N^2/2 次的交换;
+/// 如果是乱序的, 大概需要 N^2/4 次的比较, 以及 N^2/4 次的交换.
+pub fn insertion_sort<T>(list: &mut [T])
+where
+    T: PartialOrd,
+{
+    let len = list.len();
+    for i in 1..len {
+        for j in (1..=i).rev() {
+            if list[j - 1] > list[j] {
+                list.swap(j - 1, j);
+            } else {
+                break;
+            }
+        }
+    }
+}

sorts/src/lib.rs

@@ -10,5 +10,8 @@
     clippy::pedantic
 )]
 
+mod insertion_sort;
+pub use insertion_sort::insertion_sort;
+
 mod selection_sort;
 pub use selection_sort::selection_sort;