Implementing leftist heap.

2022/03/algorithms/leftist_heap.js

@@ -0,0 +1,77 @@
+"use strict";
+
+// const fs = require('fs');
+// const {EOL} = require('os');
+
+function log(v) {
+	// console.log(v);
+}
+
+function merge_heap(a, b) {
+	log('a', a);
+	log('b', b);
+	if (!a) {
+		log('a is empty. Returning b');
+		return b;
+	}
+
+	if (!b) {
+		log('b is empty. Returning a');
+		return a;
+	}
+
+	// a & b are non null
+
+	if (a.value > b.value) {
+		log(`a.value is bigger than b.value`);
+		return merge_heap(b, a); // heap the top, the smallest
+	}
+
+	log('Merging a.right with b');
+	a.right = merge_heap(a.right, b); // merging right as right is usually smaller
+	// and should be more performent thus
+	// a.right is not null as b is not null
+	if (!a.left) {
+		a.left = a.right;
+		a.right = null;
+		a.height = 1;
+		return a; // a is already merged with b and having null right
+	}
+
+	let t;
+	// we keep leftist tree intact as it's balanced to the left
+	if (a.left.height < a.right.height) {
+		t = a.left;
+		a.left = a.right;
+		a.right = t;
+	}
+
+	a.height = a.right.height + 1;
+	return a;
+}
+
+function pop_heap(heap) {
+	return merge_heap(heap.left, heap.right);
+}
+
+function insert_heap(heap, val) {
+	return merge_heap(heap, {value: val, height: 0});
+}
+
+let values = [10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0];
+let heap = {root: null};
+
+// heap.root = merge_heap(heap.root, {value: 1, height: 1});
+// heap.root = merge_heap(heap.root, {value: 2, height: 1});
+// heap.root = merge_heap(heap.root, {value: 3, height: 1});
+// heap.root = merge_heap(heap.root, {value: -1, height: 1});
+
+for (let el of values) {
+	heap.root = merge_heap(heap.root, {value: el, height: 1});
+}
+
+while (heap.root) {
+	let el = heap.root.value;
+	console.log(`Value: ${el}`);
+	heap.root = pop_heap(heap.root);
+}