堆排序和topN算法:

topN算法，第一次调用topN，然后把海量数据一次和小顶堆第一个比较，如果>第一个元素，就交换，然后调用minHeapify方法排序一遍。

然后比较下一个数据。

public class HeapSortAndTopN {

public static void main(String[] args) {

int[] arr = new int[]{3,5,3,0,8,6,1,5,8,6,2,4,9,4,7,0,1,8,9,7,3,1,2,5,9,7,4,0,2,6};

new HeapSortAndTopN().sort(arr);

System.out.println(Arrays.toString(arr));

}

public void sort(int[] a) {

int len = a.length;

int firstNonLeafIndex = (len - 2)/2;

for(int i = firstNonLeafIndex; i >=0 ; i --) {

maxHeapify(a,len,i);

}

for(int j = len - 1; j > 0 ; j --) {

swap(a,j,0);

maxHeapify(a,j,0);

}

}

private void maxHeapify(int[] a, int len, int subTreeNodeMax) {

int left = subTreeNodeMax * 2 + 1;

int right = subTreeNodeMax * 2 + 2;

int maxIndex = subTreeNodeMax;

if(left < len && a[left] > a[maxIndex]) {

maxIndex = left;

}

if(right < len && a[right] > a[maxIndex]) {

maxIndex = right;

}

if(maxIndex != subTreeNodeMax) {

swap(a, maxIndex, subTreeNodeMax);

maxHeapify(a, len, maxIndex);

}

}

private void minHeapify(int[] a, int len, int subTreeNodeMax) {

int left = subTreeNodeMax * 2 + 1;

int right = subTreeNodeMax * 2 + 2;

int maxIndex = subTreeNodeMax;

if(left < len && a[left] < a[maxIndex]) {

maxIndex = left;

}

if(right < len && a[right] < a[maxIndex]) {

maxIndex = right;

}

if(maxIndex != subTreeNodeMax) {

swap(a, maxIndex, subTreeNodeMax);

maxHeapify(a, len, maxIndex);

}

}

private void swap(int[] a, int i, int j) {

int t = a[i];

a[i] = a[j];

a[j] = t;

}

public int[] topN(int[] array) {

if(array != null && array.length > 0) {

int arrayLen = array.length;

int firtNonLeafIndex = (arrayLen - 2) / 2;

for(int i = firtNonLeafIndex; i >= 0 ; i --) {

minHeapify(array, arrayLen, i);

}

}

return array;

}

}