java 堆排序

import java.util.Arrays;

public class HeapSort {

    public static void heapSort(int[] arr) {
        int n = arr.length;

        // Build max heap
        for (int i = n / 2 - 1; i >= 0; i--) {
            heapify(arr, n, i);
        }

        // Extract elements from heap one by one
        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[]
    private static void heapify(int[] arr, int n, int i) {
        int largest = i; // Initialize largest as root
        int left = 2 * i + 1; // left child
        int right = 2 * i + 2; // right child

        // If left child is larger than root
        if (left < n && arr[left] > arr[largest]) {
            largest = left;
        }

        // If right child is larger than largest so far
        if (right < n && arr[right] > arr[largest]) {
            largest = right;
        }

        // 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);
        }
    }

    // Driver code to test above
    public static void main(String[] args) {
        int[] arr = {12, 11, 13, 5, 6, 7};
        System.out.println("Original array: " + Arrays.toString(arr));

        heapSort(arr);

        System.out.println("Sorted array: " + Arrays.toString(arr));
    }
}

解释说明：

1. 构建最大堆：首先，我们将数组构建成一个最大堆。最大堆的特性是每个节点的值都大于或等于其子节点的值。
2. 堆排序过程：将最大堆的根节点（即最大值）与堆的最后一个元素交换，然后减少堆的大小，并对新的根节点进行 heapify 操作以保持最大堆的性质。重复此过程直到堆的大小为1。
3. heapify函数：用于维护最大堆的性质。它确保以某个节点为根的子树满足最大堆的条件。
4. 主函数：创建一个示例数组并调用 heapSort 函数进行排序，最后输出排序后的数组。

希望这段代码和解释对你有帮助！