diff --git a/book/content/part02/array.asc b/book/content/part02/array.asc
index 3bde2929..25c029ee 100644
--- a/book/content/part02/array.asc
+++ b/book/content/part02/array.asc
@@ -73,7 +73,7 @@ Here's an example:
 [source, javascript]
 ----
 const array = [2, 5, 1];
-array.unshift(0); // ↪️ 8
+array.unshift(0); // ↪️ 4
 console.log(array); // [ 0, 2, 5, 1 ]
 array.unshift(-2, -1); // ↪️ 6
 console.log(array); // [ -2, -1, 0, 2, 5, 1 ]
diff --git a/src/data-structures/heaps/heap.js b/src/data-structures/heaps/heap.js
index 54863c39..537894ee 100644
--- a/src/data-structures/heaps/heap.js
+++ b/src/data-structures/heaps/heap.js
@@ -59,7 +59,7 @@ class Heap {
    */
   bubbleUp() {
     let index = this.size - 1;
-    const parent = (i) => Math.ceil(i / 2 - 1);
+    const parent = (i) => Math.ceil(i / 2) - 1;
     while (parent(index) >= 0 && this.comparator(parent(index), index) > 0) {
       this.swap(parent(index), index);
       index = parent(index);