[array] add bubblesortItem

Author: dmonad

array.js

@@ -182,3 +182,39 @@ export const map = (arr, mapper) => {
   }
   return /** @type {any} */ (res)
 }
+
+/**
+ * This function bubble-sorts a single item to the correct position. The sort happens in-place and
+ * might be useful to ensure that a single item is at the correct position in an otherwise sorted
+ * array.
+ *
+ * @example
+ *  const arr = [3, 2, 5]
+ *  arr.sort((a, b) => a - b)
+ *  arr // => [2, 3, 5]
+ *  arr.splice(1, 0, 7)
+ *  array.bubbleSortItem(arr, 1, (a, b) => a - b)
+ *  arr // => [2, 3, 5, 7]
+ *
+ * @template T
+ * @param {Array<T>} arr
+ * @param {number} i
+ * @param {(a:T,b:T) => number} compareFn
+ */
+export const bubblesortItem = (arr, i, compareFn) => {
+  const n = arr[i]
+  let j = i
+  // try to sort to the right
+  while (compareFn(n, arr[j + 1]) > 0) {
+    arr[j] = arr[j + 1]
+    arr[++j] = n
+  }
+  if (i === j && j > 0) { // no change yet
+    // sort to the left
+    while (compareFn(arr[j - 1], n) > 0) {
+      arr[j] = arr[j - 1]
+      arr[--j] = n
+    }
+  }
+  return j
+}

array.test.js

@@ -1,5 +1,6 @@
 import * as array from './array.js'
 import * as t from './testing.js'
+import * as prng from './prng.js'
 
 /**
  * @param {t.TestCase} _tc
@@ -117,3 +118,29 @@ export const testUnique = _tc => {
   t.compare([{ el: 1 }], array.uniqueBy([{ el: 1 }, { el: 1 }], o => o.el))
   t.compare([], array.uniqueBy([], o => o))
 }
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRepeatBubblesortItem = tc => {
+  const arr = Array.from(prng.uint8Array(tc.prng, 10))
+  arr.sort((a, b) => a - b)
+  const newItem = prng.uint32(tc.prng, 0, 256)
+  const pos = prng.uint32(tc.prng, 0, arr.length)
+  arr.splice(pos, newItem)
+  const arrCopySorted = arr.slice().sort((a, b) => a - b)
+  array.bubblesortItem(arr, pos, (a, b) => a - b)
+  t.compare(arr, arrCopySorted)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRepeatBubblesort = tc => {
+  const arr = Array.from(prng.uint8Array(tc.prng, 10))
+  const arrCopySorted = arr.slice().sort((a, b) => a - b)
+  for (let i = arr.length - 1; i >= 0; i--) {
+    while (array.bubblesortItem(arr, i, (a, b) => a - b) !== i) { /* nop */ }
+  }
+  t.compare(arr, arrCopySorted)
+}

test.html

@@ -28,7 +28,7 @@
   "lib0/component": "./component.js",
   "lib0/conditions.js": "./conditions.js",
   "lib0/dist/conditions.cjs": "./dist/conditions.cjs",
-  "lib0/conditions": "./condititons.js",
+  "lib0/conditions": "./conditions.js",
   "lib0/crypto/jwt": "./crypto/jwt.js",
   "lib0/crypto/aes-gcm": "./crypto/aes-gcm.js",
   "lib0/crypto/ecdsa": "./crypto/ecdsa.js",