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# Java Program for Heap Sort

• Difficulty Level : Medium
• Last Updated : 27 Mar, 2019

Heap sort is a comparison based sorting technique based on Binary Heap data structure. It is similar to selection sort where we first find the maximum element and place the maximum element at the end. We repeat the same process for remaining element.

## Java

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 `// Java program for implementation of Heap Sort``public` `class` `HeapSort``{``    ``public` `void` `sort(``int` `arr[])``    ``{``        ``int` `n = arr.length;`` ` `        ``// Build heap (rearrange array)``        ``for` `(``int` `i = n / ``2` `- ``1``; i >= ``0``; i--)``            ``heapify(arr, n, i);`` ` `        ``// One by one extract an element from heap``        ``for` `(``int` `i=n-``1``; i>=``0``; i--)``        ``{``            ``// Move current root to end``            ``int` `temp = arr[``0``];``            ``arr[``0``] = arr[i];``            ``arr[i] = temp;`` ` `            ``// call max heapify on the reduced heap``            ``heapify(arr, i, ``0``);``        ``}``    ``}`` ` `    ``// To heapify a subtree rooted with node i which is``    ``// an index in arr[]. n is size of heap``    ``void` `heapify(``int` `arr[], ``int` `n, ``int` `i)``    ``{``        ``int` `largest = i;  ``// Initialize largest as root``        ``int` `l = ``2``*i + ``1``;  ``// left = 2*i + 1``        ``int` `r = ``2``*i + ``2``;  ``// right = 2*i + 2`` ` `        ``// If left child is larger than root``        ``if` `(l < n && arr[l] > arr[largest])``            ``largest = l;`` ` `        ``// If right child is larger than largest so far``        ``if` `(r < n && arr[r] > arr[largest])``            ``largest = r;`` ` `        ``// If largest is not root``        ``if` `(largest != i)``        ``{``            ``int` `swap = arr[i];``            ``arr[i] = arr[largest];``            ``arr[largest] = swap;`` ` `            ``// Recursively heapify the affected sub-tree``            ``heapify(arr, n, largest);``        ``}``    ``}`` ` `    ``/* A utility function to print array of size n */``    ``static` `void` `printArray(``int` `arr[])``    ``{``        ``int` `n = arr.length;``        ``for` `(``int` `i=``0``; i

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