算法-堆排序java实现

堆(dui)排序的java实现

public class Heapsort {
    private int heap_size;
    public static void main(String[] args) {
        int[] ints = {1,6,3,9,3,8,3,443};
        Heapsort demo = new Heapsort();
        int[] arrsort = demo.heapsort(ints);
        demo.printarr(arrsort);
        int[] arrsort2 = demo.heapsort_des(ints);
        demo.printarr(arrsort);


    }

    public int[] heapsort(int[] arr) {
        //堆排序 将堆顶元素交换放到有效值的最后一位 然后再堆化交换后的堆 通过循环直至堆成从小到大排序
        buildmaxheap(arr);
        for(int i=arr.length-1;i>0;i--){
            int temp = arr[0];
            arr[0]=arr[i];
            arr[i]=temp;
            heap_size=heap_size-1;
            heapify(arr,0);
        }
        return arr;

    }
    public int[] heapsort_des(int[] arr) {
        //堆排序 将堆顶元素交换放到有效值的最后一位 然后再堆化交换后的堆 通过循环直至堆成从小到大排序 再逆序数组
        buildmaxheap(arr);
        for(int i=arr.length-1;i>0;i--){
            int temp = arr[0];
            arr[0]=arr[i];
            arr[i]=temp;
            heap_size=heap_size-1;
            heapify(arr,0);
        }
        int temp;
        for(int i=0;i<arr.length/2;i++){
            temp=arr[i];
            arr[i]=arr[(arr.length-i-1)];
            arr[(arr.length-i-1)]=temp;
        }
        return arr;

    }

    public void printarr(int[] arr) {

        for (int i = 0; i < arr.length; i++) {
            System.out.print(arr[i]+" ");
        }
        System.out.println("");
    }

    public void buildmaxheap(int[] arr) {
        //构建大顶堆
        heap_size=arr.length;
        for (int i = ((arr.length-1) / 2); i > -1; i--) {
            heapify(arr, i);
        }
    }

    public void heapify(int[] arr, int i) {
        //堆化arr数组通过递归保证i和其所有子节点都满足最大堆的性质
        int l = left(i);
        int r = right(i);
        int largest = i;
        if (l < heap_size && arr[l] > arr[i]) {
            largest = l;
        }
        if (r < heap_size && arr[r] > arr[largest]) {
            largest = r;
        }
        if (largest != i) {
            int temp = arr[i];
            arr[i] = arr[largest];
            arr[largest] = temp;
            heapify(arr, largest);
        }
    }

    public int left(int i) {
        return 2 * i;
    }

    public int right(int i) {
        return 2 * i + 1;
    }
}