基于Java实现堆排序

堆排序

public static void heapSort(int[] arr) {
if (arr == null || arr.length < 2) {
return;
}
for (int i = 0; i < arr.length; i++) {
heapInsert(arr, i);
}
int size = arr.length;
swap(arr, 0, --size); //0号位置的元素最大，换到最后.siez-1
while (size > 0) {
heapify(arr, 0, size);
swap(arr, 0, --size);
}
}

//建成大头堆，从下往上调
public static void heapInsert(int[] arr, int index) {
while(arr[index] > arr[(index - 1) / 2] ){
swap(arr,index,(index - 1) / 2);
index = (index - 1) / 2;
}
}

//从上往下调
public static void heapify(int[] arr, int index, int size) {
int left = index * 2 + 1;
while(left < size){
int largest = left + 1 < size && arr[left + 1] > arr[left] ? left + 1 : left;
largest = arr[index] > arr[largest] ? index : largest;
if(largest == index){
break;
}
swap(arr,largest,index);
index = largest;
left = index * 2 + 1;
}
}

public static void swap(int[] arr, int i, int j) {
int tmp = arr[i];
arr[i] = arr[j];
arr[j] = tmp;
}