Add mergesort

snippets/mergeSort.md

@@ -0,0 +1,30 @@
+---
+title: mergeSort
+tags: algorithm,array,recursion,advanced
+---
+
+Sorts an array of numbers, using the merge sort algorithm.
+
+- Use recursion.
+- If the `length` of the array is less than `2`, return the array.
+- Use `Math.floor()` to calculate the middle point of the array.
+- Use `Array.prototype.slice()` to slice the array in two and recursively call `mergeSort()` on the created subarrays.
+- Finally, use `Array.from()` and `Array.prototype.shift()` to combine the two sorted subarrays into one.
+
+```js
+const mergeSort = arr => {
+  if (arr.length < 2) return arr;
+  const mid = Math.floor(arr.length / 2);
+  const l = mergeSort(arr.slice(0, mid));
+  const r = mergeSort(arr.slice(mid, arr.length));
+  return Array.from({ length: l.length + r.length }, () => {
+    if (!l.length) return r.shift();
+    else if (!r.length) return l.shift();
+    else return l[0] > r[0] ? r.shift() : l.shift();
+  });
+};
+```
+
+```js
+mergeSort([5, 1, 4, 2, 3]); // [1, 2, 3, 4, 5]
+```