java 数据结构之堆排序（HeapSort）详解及实例

publicclassHeapSort {

  publicstaticvoidmain(String[] args) {

    int[] arr = {3,2,1,0, -1, -2, -3};

    System.out.println("Before heap:");

    printArray(arr);

    heapSort(arr);

    System.out.println("After heap sort:");

    printArray(arr);

  }

  publicstaticvoidheapSort(int[] arr) {

    if(arr ==null|| arr.length <=1) {

      return;

    }

    buildMaxHeap(arr);//构建最大堆

    for(inti = arr.length -1; i >=1; i--) {

      exchangeElements(arr,0, i);//交换堆顶和第0位置元素

      maxHeap(arr, i,0);//因为交换元素后，有可能违反堆的性质，所以沉降元素

    }

  }

  privatestaticvoidbuildMaxHeap(int[] arr) {//构建最大堆

    if(arr ==null|| arr.length <=1) {

      return;

    }

    inthalf = arr.length /2;

    for(inti = half; i >=0; i--) {

      maxHeap(arr, arr.length, i);

    }

  }

  privatestaticvoidmaxHeap(int[] arr,intheapSize,intindex) {

    intleft = index *2+1;//左子树上的元素

    intright = index *2+2;//右子树上的元素

    intlargest = index;//初始化最大元素

    if(left < heapSize && arr[left] > arr[index]) {

      largest = left;

    }

    if(right < heapSize && arr[right] > arr[largest]) {

      largest = right;

    }

    if(index != largest) {//判断根元素是否为最大元素

      exchangeElements(arr, index, largest);

      maxHeap(arr, heapSize, largest);

    }

  }

  publicstaticvoidprintArray(int[] arr) {//打印数组

    System.out.print("{");

    for(inti =0; i < arr.length; i++) {

      System.out.print(arr[i]);

      if(i < arr.length -1) {

        System.out.print(", ");

      }

    }

    System.out.println("}");

  }

  publicstaticvoidexchangeElements(int[] arr,intindex1,intindex2) {//交换元素

    inttemp = arr[index1];

    arr[index1] = arr[index2];

    arr[index2] = temp;

  }

}