new post: Sort Algorithm 2

source/_posts/Sort-Algorithm（2）：-Elementary-Sort-Javascript-Implement-Shell-Sort.md

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+---
+title: Sort Algorithm（2）： Elementary Sort Javascript Implement - Shell Sort
+date: 2024-03-23 20:30:41
+tags: [Javascript, Algorithm, Sort]
+---
+
+Shell Sort is a very efficient sorting algorithm; its time complexity can almost reach O(n) in real-world production.
+
+The code Shell Sort moves elements in the same way as Selection Sort, but it seeks local sorting and then achieves global sorting.
+
+Let's see How it works:
+
+```
+var { less } = require("./Shuffle");
+
+function shellSort(a) {
+  var length = a.length;
+  var h = 1;
+  while (h < Math.floor(length / 3)) h = 3 * h + 1; //3x + 1 increament
+
+  while (h >= 1) {
+    for (let i = h; i < length; i++) {
+      // h-insertion_sort
+      for (let j = i; j >= h && less(a[j], a[j - h]); j -= h) {
+        let temp = a[j - h];
+        a[j - h] = a[j];
+        a[j] = temp;
+      }
+    }
+    h = Math.floor(h / 3); // next increament
+  }
+}
+
+module.exports = shellSort;
+```
+
+Why is Shell Sort so effective compared to Selection Sort? It 
+moves elements in multiple positions, the number of increments every time, but Selection Sort moves elements in only one position.
+
+Shell Sort is more simple than Quick Sort, so the application is widespread in small embedded devices.