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Minimum priority queue added alongside heap sort implementation #548

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Oct 10, 2018
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Minimum priority queue added alongside heap sort implementation #548

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131 changes: 131 additions & 0 deletions DataStructures/Heaps/MinPriorityQueue.java
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/* Minimum Priority Queue
* It is a part of heap data structure
* A heap is a specific tree based data structure
* in which all the nodes of tree are in a specific order.
* that is the children are arranged in some
* respect of their parents, can either be greater
* or less than the parent. This makes it a min priority queue
* or max priority queue.
*/

// Functions: insert, delete, peek, isEmpty, print, heapSort, sink

public class MinPriorityQueue {
private int[] heap;
private int capacity;
private int size;

// calss the constructor and initializes the capacity
MinPriorityQueue(int c) {
this.capacity = c;
this.size = 0;
this.heap = new int[c + 1];
}

// inserts the key at the end and rearranges it
// so that the binary heap is in appropriate order
public void insert(int key) {
if (this.isFull())
return;
this.heap[this.size + 1] = key;
int k = this.size + 1;
while (k > 1) {
if (this.heap[k] < this.heap[k / 2]) {
int temp = this.heap[k];
this.heap[k] = this.heap[k / 2];
this.heap[k / 2] = temp;
}
k = k / 2;
}
this.size++;
}

// returns the highest priority value
public int peek() {
return this.heap[1];
}

// returns boolean value whether the heap is empty or not
public boolean isEmpty() {
if (0 == this.size)
return true;
return false;
}

// returns boolean value whether the heap is full or not
public boolean isFull() {
if (this.size == this.capacity)
return true;
return false;
}

// prints the heap
public void print() {
for (int i = 1; i <= this.capacity; i++)
System.out.print(this.heap[i] + " ");
System.out.println();
}

// heap sorting can be done by performing
// delete function to the number of times of the size of the heap
// it returns reverse sort because it is a min priority queue
public void heapSort() {
for (int i = 1; i < this.capacity; i++)
this.delete();
}

// this function reorders the heap after every delete function
private void sink() {
int k = 1;
while (2 * k <= this.size || 2 * k + 1 <= this.size) {
int minIndex;
if (this.heap[2 * k] >= this.heap[k]) {
if (2 * k + 1 <= this.size && this.heap[2 * k + 1] >= this.heap[k]) {
break;
} else if (2 * k + 1 > this.size) {
break;
}
}
if (2 * k + 1 > this.size) {
minIndex = this.heap[2 * k] < this.heap[k] ? 2 * k : k;
} else {
if (this.heap[k] > this.heap[2 * k] || this.heap[k] > this.heap[2 * k + 1]) {
minIndex = this.heap[2 * k] < this.heap[2 * k + 1] ? 2 * k : 2 * k + 1;
} else {
minIndex = k;
}
}
int temp = this.heap[k];
this.heap[k] = this.heap[minIndex];
this.heap[minIndex] = temp;
k = minIndex;
}
}

// deletes the highest priority value from the heap
public int delete() {
int min = this.heap[1];
this.heap[1] = this.heap[this.size];
this.heap[this.size] = min;
this.size--;
this.sink();
return min;
}

public static void main(String[] args) {
// testing
MinPriorityQueue q = new MinPriorityQueue(8);
q.insert(5);
q.insert(2);
q.insert(4);
q.insert(1);
q.insert(7);
q.insert(6);
q.insert(3);
q.insert(8);
q.print(); // [ 1, 2, 3, 5, 7, 6, 4, 8 ]
q.heapSort();
q.print(); // [ 8, 7, 6, 5, 4, 3, 2, 1 ]
}
}