D堆的实现

实现上一篇博客(http://blog.csdn.net/buleriver/article/details/38469977)说的D堆。假设把mD设置成2。D堆就退化成二叉堆，也就是说。二叉堆是D堆的一种情况。

public class DHeap {
    public static final int INIT_CAPACITY = 10;
    private int[] mArray;
    private int mLength;
    private final int mD;  

    public DHeap(int d) {
        mArray = new int[INIT_CAPACITY + 1];
        mLength = 0;
        mD = d;
    }  

    public int getParentIndex(int index) {
        return (index - 2 + mD) / mD;
    }  

    public int getChildIndex(int pIndex, int childIndex) {
        return mD * (pIndex - 1) + 2 + childIndex;
    }  

    private void expandArray(int length) {
        int[] arr = new int[length];
        System.arraycopy(mArray, 1, arr, 1, mLength);
        mArray = arr;
    }  

    /**
     * 自下而上，把value放到最后一个，然后一直和其父节点交换，找到合适的位置
     */
    public void insert(int value) {
        if (mLength >= mArray.length - 1) {
            expandArray(mArray.length * 2);
        }
        mArray[++mLength] = value;
        int index = mLength;
        int parentIndex = getParentIndex(index);
        while (parentIndex > 0) {
            int currentValue = mArray[index];
            int parentValue = mArray[parentIndex];
            if (currentValue < parentValue) {
                mArray[parentIndex] = currentValue;
                mArray[index] = parentValue;
                index = parentIndex;
                parentIndex = getParentIndex(index);
            } else {
                break;
            }
        }
    }  

    public void deleteMin() {
        if (mLength <= 0) {
            return;
        } else if (mLength == 1) {
            mLength--;
        } else {
            mArray[1] = mArray[mLength];
            int index = 1;
            mLength--;
            while (true) {
                int value = mArray[index];
                int minIndex = -1;  // 最小孩子的数组索引
                boolean lastLevel = false;  // 是否已经到了最底层
                int firstChildIndex = getChildIndex(index, 0);
                int lastChildIndex = firstChildIndex + mD;
                for (int childIndex = firstChildIndex; childIndex < lastChildIndex; childIndex++) {  // 找到最小的孩子
                    if (childIndex > mLength) {  // 已经到了最后一个
                        lastLevel = true;
                        break;
                    }
                    int childValue = mArray[childIndex];
                    if (value > childValue) {
                        value = childValue;
                        minIndex = childIndex;
                    }
                }
                if (minIndex < 0) {  // 已经符合d堆的性质，不须要置换了
                    break;
                } else { // 须要置换
                    mArray[minIndex] = mArray[index];
                    mArray[index] = value;
                    index = minIndex;
                }
                if (lastLevel) {    // 已经到了最底层
                    break;
                }
            }
        }
    }
}