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How to perform heapsort on an array in Java?
Following is the algorithm for heapsort (maxheap).
Step 1 − Create a new node at the end of the heap.
Step 2 − Assign new value to the node.
Step 3 − Compare the value of this child node with its parent.
Step 4 − If the value of parent is less than a child, then swap them.
Step 5 − Repeat step 3 & 4 until Heap property holds.
Example
import java.util.Arrays;
import java.util.Scanner;
public class Heapsort {
public static void heapSort(int[] myArray, int length) {
int temp;
int size = length-1;
for (int i = (length / 2); i >= 0; i--) {
heapify(myArray, i, size);
};
for(int i= size; i>=0; i--) {
temp = myArray[0];
myArray[0] = myArray[size];
myArray[size] = temp;
size--;
heapify(myArray, 0, size);
}
System.out.println(Arrays.toString(myArray));
}
public static void heapify (int [] myArray, int i, int heapSize) {
int a = 2*i;
int b = 2*i+1;
int largestElement;
if (a<= heapSize && myArray[a] > myArray[i]) {
largestElement = a;
} else {
largestElement = i;
}
if (b <= heapSize && myArray[b] > myArray[largestElement]) {
largestElement = b;
}
if (largestElement != i) {
int temp = myArray[i];
myArray[i] = myArray[largestElement];
myArray[largestElement] = temp;
heapify(myArray, largestElement, heapSize);
}
}
public static void main(String args[]) {
Scanner scanner = new Scanner(System.in);
System.out.println("Enter the size of the array :: ");
int size = scanner.nextInt();
System.out.println("Enter the elements of the array :: ");
int[] myArray = new int[size];
for(int i=0; i<size; i++) {
myArray[i] = scanner.nextInt();
}
heapSort(myArray, size);
}
}Output
Enter the size of the array :: 5 Enter the elements of the array :: 45 125 44 78 1 [1, 44, 45, 78, 125]
Updated on: 19-Feb-2020
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