heap_implementation.js

/* 
	Author : Samir Paul

*/
// export { MinHeap }
class MinHeap {
    constructor() {
        this.heap_array = [];
    }

    /// returns size of the min heap 
    size() {
        return this.heap_array.length;
    }

    /// returns if the heap is empty 
    empty() {
        return (this.size() === 0);
    }
 
    /// insert a new value in the heap 
    push(value) {
        this.heap_array.push(value);
        this.up_heapify();
    }

    /// updates heap by up heapifying
    up_heapify() {
        var current_index = this.size() - 1;
        while (current_index > 0) {
            var current_element = this.heap_array[current_index];
            var parent_index = Math.trunc((current_index - 1) / 2);
            var parent_element = this.heap_array[parent_index];

            if (parent_element[0] < current_element[0]) {
                break;
            }
            else {
                this.heap_array[parent_index] = current_element;
                this.heap_array[current_index] = parent_element;
                current_index = parent_index;
            }
        }
    }

    /// returns the top element (smallest value element)
    top() {
        return this.heap_array[0];
    }

    /// delete the top element
    pop() {
        if (this.empty() == false) {
            var last_index = this.size() - 1;
            this.heap_array[0] = this.heap_array[last_index];
            this.heap_array.pop();
            this.down_heapify();
        }
    }

    /// updates heap by down heapifying
    down_heapify() {
        var current_index = 0;
        var current_element = this.heap_array[0];
        while (current_index < this.size()) {
            var child_index1 = (current_index * 2) + 1;
            var child_index2 = (current_index * 2) + 2;
            if (child_index1 >= this.size() && child_index2 >= this.size()) {
                break;
            }
            else if (child_index2 >= this.size()) {
                let child_element1 = this.heap_array[child_index1];
                if (current_element[0] < child_element1[0]) {
                    break;
                }
                else {
                    this.heap_array[child_index1] = current_element;
                    this.heap_array[current_index] = child_element1;
                    current_index = child_index1;
                }
            }
            else {
                var child_element1 = this.heap_array[child_index1];
                var child_element2 = this.heap_array[child_index2];
                if (current_element[0] < child_element1[0] && current_element[0] < child_element2[0]) {
                    break;
                }
                else {
                    if (child_element1[0] < child_element2[0]) {
                        this.heap_array[child_index1] = current_element;
                        this.heap_array[current_index] = child_element1;
                        current_index = child_index1;
                    }
                    else {
                        this.heap_array[child_index2] = current_element;
                        this.heap_array[current_index] = child_element2;
                        current_index = child_index2;
                    }
                }
            }
        }
    }
}