数据结构和算法(15)之堆排序

学习数据结构和算法的日常Demo

堆排序基本介绍

堆排序基本思想

堆排序步骤图解

简单总结

代码实现:

public class 堆排序 {
    public static void main(String args[]) {
        int a[] = {6, 2, 32, 43, 8, 16, 21, 9, 77};
        heapSort(a);
        System.out.println(Arrays.toString(a));
    }

    public static void heapSort(int[] array) {
        if (array == null || array.length <= 1) {
            return;
        }
        buildMaxHeap(array);//建立最大堆
        for (int i = array.length - 1; i >= 1; i--) {
            //最大的在0位置，那么开始沉降，这样每交换一次最大的值就丢到最后了
            exchangeElements(array, 0, i);
            //继续获取0位置最大值
            maxHeap(array, i, 0);
        }
    }

    //(2)		//建立最大堆
    private static void buildMaxHeap(int[] array) {
        if (array == null || array.length <= 1) {
            return;
        }
        int half = (array.length - 1) / 2;
        for (int i = half; i >= 0; i--) {
            maxHeap(array, array.length, i);
        }
    }

    private static void maxHeap(int[] array, int heapSize, int index) {
        int left = index * 2 + 1;
        int right = index * 2 + 2;
        int largest = index;
        if (left < heapSize && array[left] > array[index]) {
            largest = left;
        }
        if (right < heapSize && array[right] > array[largest]) {
            largest = right;
        }
        if (index != largest) {
            exchangeElements(array, index, largest);

            maxHeap(array, heapSize, largest);
        }
    }


    public static void exchangeElements(int[] array, int index1, int index2) {
        int temp = array[index1];
        array[index1] = array[index2];
        array[index2] = temp;
    }
}

GitHub:数据结构和算法源代码