Binary array heap implementation with bottom up initialization.

2022/03/algorithms/heap_binary_arr.js

@@ -0,0 +1,133 @@
+"use strict";
+
+// const fs = require('fs');
+// const {EOL} = require('os');
+
+//    0
+//  1   2
+// 3 4 5 6
+
+//  |--- i ---|
+// 2*i+1   2*i+2
+
+function check_heap(arr) {
+	// parent has to be smaller or equal
+	let n = arr.length;
+	for (let i = n - 1; i > 0; i--) {
+		let idx = (i-1) >> 1;
+		if (heap[idx] > heap[i]) {
+			return [idx, i];
+		}
+	}
+
+	return [-1, -1];
+}
+
+function push_up(heap, i) {
+	let idx, t;
+	while (i > 0) {
+		idx = (i - 1) >> 1;
+		console.log(`Checking ${i} with parent ${idx}. v ${heap[i]} vs p ${heap[idx]}`);
+		if (heap[idx] > heap[i]) {
+			console.log(`Replacing ${i}(${heap[i]}) with ${idx}(${heap[idx]})`);
+			t = heap[idx];
+			heap[idx] = heap[i];
+			heap[i] = t;
+			i = idx;
+		} else {
+			break;
+		}
+	}
+}
+
+function push_down(heap, i) {
+	let t;
+
+	while (true) {
+		if (i + 1 >= heap.length) {
+			// we are the last. No children
+			return;
+		}
+
+		if ((2*i + 1 >= heap.length || heap[i] < heap[2*i+1]) 
+				&& (2*i + 2 >= heap.length || heap[i] < heap[2*i+2])) {
+			// heap conditions are right
+			return;
+		}
+
+		// let's replace it with the smallest
+
+		//  -1       5
+		// 0  1 ->  0  1
+
+		if (2*i + 2 < heap.length) {
+			if (heap[2*i+1] > heap[2*i+2]) {
+				// heap[2*i+2] is smallest
+				t = heap[2*i+2];
+				heap[2*i+2] = heap[i];
+				heap[i] = t;
+				i = 2*i + 2;
+			} else {
+				// heap[2*i+1] is smallest
+				t = heap[2*i+1];
+				heap[2*i+1] = heap[i];
+				heap[i] = t;
+				i = 2*i + 1;
+			}
+		} else {
+			// we have only one case possible
+			// heap[2*i+1] is smallest
+				t = heap[2*i+1];
+				heap[2*i+1] = heap[i];
+				heap[i] = t;
+				i = 2*i + 1;
+		}
+	}
+
+}
+
+function insert_heap(heap, el) {
+	let n = heap.length;
+	heap[n] = el;
+	push_up(heap, n);
+}
+
+function pop_heap(heap) {
+	let n = heap.length;
+	let el = heap[0];
+	heap[0] = heap[n-1];
+	heap.pop();
+	push_down(heap, 0);
+	return el;
+}
+
+function build_heap(arr) {
+	const n = arr.length;
+	const heap = new Array(n);
+	for (let i = 0; i < n; i++) {
+		heap[i] = arr[i];
+	}
+
+	let t;
+	for (let i = n - 1; i > 0; i--) {
+		push_up(heap, i);
+	}
+
+	return heap;
+}
+
+const arr = [6, 5, 4, 3, 2, 1, 0];
+console.log('Heap 1', arr);
+const heap = build_heap(arr);
+
+insert_heap(heap, 7);
+insert_heap(heap, 8);
+insert_heap(heap, 9);
+insert_heap(heap, 10);
+
+console.log('Heap 2', heap);
+console.log('Check heap', check_heap(heap));
+
+while (heap.length) {
+	console.log(pop_heap(heap));
+}