堆排序：利用大根堆

数组全部入堆，再出堆从后向前插入回数组中，数组就从小到大有序了。

public class MaxHeap<T extends Comparable<? super T>> { private T[] data; private int size; private int capacity; public MaxHeap(int capacity) { this.data = (T[]) new Comparable[capacity + 1]; size = 0; this.capacity = capacity; } public int size() { return this.size; } public boolean isEmpty() { return size == 0; } public int getCapacity() { return this.capacity; } /** * @return 查看最大根(只看不删, 与popMax对比) */ public T seekMax() { return data[1]; } public void swap(int i, int j) { if (i != j) { T temp = data[i]; data[i] = data[j]; data[j] = temp; } } public void insert(T item) { size++; data[size] = item; shiftUp(size); } /** * @return 弹出最大根(弹出意味着删除, 与seekMax对比) */ public T popMax() { swap(1, size--); shiftDown(1); return data[size + 1]; } /** * @param child 孩子节点下角标是child，父节点下角表是child/2 */ public void shiftUp(int child) { while (child > 1 && data[child].compareTo(data[child / 2]) > 0) { swap(child, child / 2); child = child / 2; } } /** * @param a data数组中某个元素的下角标 * @param b data数组中某个元素的下角标 * @return 哪个元素大就返回哪个的下角标 */ private int max(int a, int b) { if (data[a].compareTo(data[b]) < 0) {//如果data[b]大 return b;//返回b } else {//如果data[a]大 return a;//返回a } } /** * @param a data数组中某个元素的下角标 * @param b data数组中某个元素的下角标 * @param c data数组中某个元素的下角标 * @return 哪个元素大就返回哪个的下角标 */ private int max(int a, int b, int c) { int biggest = max(a, b); biggest = max(biggest, c); return biggest; } /** * @param father 父节点下角标是father,左右两个孩子节点的下角表分别是：father*2 和 father*2+1 */ public void shiftDown(int father) { while (true) { int lchild = father * 2;//左孩子 int rchild = father * 2 + 1;//右孩子 int newFather = father;//newFather即将更新，父、左、右三个结点谁大，newFather就是谁的下角标 if (lchild > size) {//如果该father结点既没有左孩子，也没有右孩子 return; } else if (rchild > size) {//如果该father结点只有左孩子，没有右孩子 newFather = max(father, lchild); } else {//如果该father结点既有左孩子，又有右孩子 newFather = max(father, lchild, rchild); } if (newFather == father) {//说明father比两个子结点都要大，表名已经是大根堆，不用继续调整了 return; } else {//否则，还需要继续调整堆，直到满足大根堆条件为止 swap(father, newFather);//值进行交换 father = newFather;//更新father的值，相当于继续调整shiftDown(newFather) } } } public static <T extends Comparable<? super T>> void sort(T[] arr) { int len = arr.length; //入堆 MaxHeap<T> maxHeap = new MaxHeap<T>(len); for (int i = 0; i < len; i++) { maxHeap.insert(arr[i]); } //出堆 for (int i = len - 1; i >= 0; i--) { arr[i] = maxHeap.popMax(); } } public static void printArr(Object[] arr) { for (Object o : arr) { System.out.print(o); System.out.print("\t"); } System.out.println(); } public static void main(String args[]) { Integer[] arr = {3, 5, 1, 7, 2, 9, 8, 0, 4, 6}; printArr(arr);//3 5 1 7 2 9 8 0 4 6 sort(arr); printArr(arr);//0 1 2 3 4 5 6 7 8 9 }}

堆排序：对数组进行构造堆(最大堆)

public class MaxHeap<T extends Comparable<? super T>> { private T[] data; private int size; private int capacity; public MaxHeap(int capacity) { this.capacity = capacity; this.size = 0; this.data = (T[]) new Comparable[capacity + 1]; } public MaxHeap(T[] arr) {//heapify,数组建堆 capacity = arr.length; data = (T[]) new Comparable[capacity + 1]; System.arraycopy(arr, 0, data, 1, arr.length); size = arr.length; for (int i = size / 2; i >= 1; i--) { shiftDown(i); } } public int size() { return this.size; } public int getCapacity() { return this.capacity; } public boolean isEmpty() { return size == 0; } public T seekMax() { return data[1]; } public void swap(int i, int j) { if (i != j) { T temp = data[i]; data[i] = data[j]; data[j] = temp; } } public void insert(T item) { size++; data[size] = item; shiftUp(size); } public T popMax() { swap(1, size--); shiftDown(1); return data[size + 1]; } public void shiftUp(int child) { while (child > 1 && data[child].compareTo(data[child / 2]) > 0) { swap(child, child / 2); child /= 2; } } /** * @param a data数组中某个元素的下角标 * @param b data数组中某个元素的下角标 * @return 哪个元素大就返回哪个的下角标 */ private int max(int a, int b) { if (data[a].compareTo(data[b]) < 0) {//如果data[b]大 return b;//返回b } else {//如果data[a]大 return a;//返回a } } /** * @param a data数组中某个元素的下角标 * @param b data数组中某个元素的下角标 * @param c data数组中某个元素的下角标 * @return 哪个元素大就返回哪个的下角标 */ private int max(int a, int b, int c) { int biggest = max(a, b); biggest = max(biggest, c); return biggest; } public void shiftDown(int father) { while (true) { int lchild = father * 2; int rchild = father * 2 + 1; int newFather = father;//这里赋不赋值无所谓，如果把下面这个return改成break,那就必须赋值了 if (lchild > size) {//如果没有左、右孩子 return; } else if (rchild > size) {//如果没有右孩子 newFather = max(father, lchild); } else {//如果有左、右孩子 newFather = max(father, lchild, rchild); } if (newFather == father) {//如果原父结点就是三者最大，则不用继续整理堆了 return; } else {//父节点不是最大，则把大的孩子交换上来，然后继续往下堆调整，直到满足大根堆为止 swap(newFather, father); father = newFather;//相当于继续shiftDown(newFather)。假如newFather原来是father的左孩子，那就相当于shiftDown(2*father) } } } public static <T extends Comparable<? super T>> void sort(T[] arr) { int len = arr.length; MaxHeap<T> maxHeap = new MaxHeap<>(arr); for (int i = len - 1; i >= 0; i--) { arr[i] = maxHeap.popMax(); } } public static void printArr(Object[] arr) { for (Object o : arr) { System.out.print(o); System.out.print("\t"); } System.out.println(); } public static void main(String args[]) { Integer[] arr = {3, 5, 1, 7, 2, 9, 8, 0, 4, 6}; printArr(arr);//3 5 1 7 2 9 8 0 4 6 sort(arr); printArr(arr);//0 1 2 3 4 5 6 7 8 9 }}

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