最大堆(Java數組實現)

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最大堆

data[1]開始存，data[0]空著不用。也可以把data[0]當成size來用。

 

public class MaxHeap<T extends Comparable<? super T>> {    protected T[] data;    protected int size;    protected 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(只看不刪, 與popMax對比)     */    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 彈出最大根(彈出意味著刪除, 與seekMax對比)     */    public T popMax() {        swap(1, size--);        shiftDown(1);        return data[size + 1];    }    /**     * @param child 孩子節點下角標是child，父節點下角表是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數組中某個元素的下角標     * @param b data數組中某個元素的下角標     * @return 哪個元素大就返回哪個的下角標     */    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數組中某個元素的下角標     * @param b data數組中某個元素的下角標     * @param c data數組中某個元素的下角標     * @return 哪個元素大就返回哪個的下角標     */    private int max(int a, int b, int c) {        int biggest = max(a, b);        biggest = max(biggest, c);        return biggest;    }    /**     * @param father 父節點下角標是father,左右兩個孩子節點的下角表分別是：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即將更新，父、左、右三個結點誰大，newFather就是誰的下角標            if (lchild > size) {//如果該father結點既沒有左孩子，也沒有右孩子                return;            } else if (rchild > size) {//如果該father結點只有左孩子，沒有右孩子                newFather = max(father, lchild);            } else {//如果該father結點既有左孩子，又有右孩子                newFather = max(father, lchild, rchild);            }            if (newFather == father) {//說明father比兩個子結點都要大，表名已經是大根堆，不用繼續調整了                return;            } else {//否則，還需要繼續調整堆，直到滿足大根堆條件為止                swap(father, newFather);//值進行交換                father = newFather;//更新father的值，相當於繼續調整shiftDown(newFather)            }        }    }    public static void main(String[] args) {        //建立大根堆        MaxHeap<Integer> maxHeap = new MaxHeap<Integer>(100);        //向堆裡存        for (int i = 0; i < 100; i++) {            maxHeap.insert((int) (Math.random() * 100));        }        //建立數組        Integer[] arr = new Integer[100];        //從堆裡取，放進數組裡        for (int i = 0; i < 100; i++) {            arr[i] = maxHeap.popMax();            System.out.print(arr[i] + " ");        }        System.out.println();    }} 

 最大堆：shiftDown()函數與上面不一樣

public class MaxHeap<T extends Comparable<? super T>> {    protected T[] data;    protected int size;    protected int capacity;    public MaxHeap(int capacity) {        data = (T[]) new Comparable[capacity + 1];        this.capacity = capacity;        size = 0;    }    public int size() {        return size;    }    public boolean isEmpty() {        return size == 0;    }    public void insert(T item) {        data[size + 1] = item;        size++;        shiftUp(size);    }    /**     * @return 彈出最大根(彈出意味著刪除, 與seekMax對比)     */    public T popMax() {        T ret = data[1];        swap(1, size);        size--;        shiftDown(1);        return ret;    }    /**     * @return 查看最大根(只看不刪, 與popMax對比)     */    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 shiftUp(int k) {        while (k > 1 && data[k / 2].compareTo(data[k]) < 0) {            swap(k, k / 2);            k /= 2;        }    }    public void shiftDown(int father) {        while (2 * father <= size) {            int newFather = 2 * father;            if (newFather + 1 <= size && data[newFather + 1].compareTo(data[newFather]) > 0) {//data[j] data[j+1]兩者取大的那個                newFather = newFather + 1;            }            if (data[father].compareTo(data[newFather]) >= 0) {                break;            } else {                swap(father, newFather);//值進行交換                father = newFather;//newFather是(2*father)或者是(2*father+1),也就是繼續shiftDown(newFather);            }        }    }    public static void main(String[] args) {        //建立大根堆        MaxHeap<Integer> maxHeap = new MaxHeap<Integer>(100);        //向堆裡存        for (int i = 0; i < 100; i++) {            maxHeap.insert((int) (Math.random() * 100));        }        //建立數組        Integer[] arr = new Integer[100];        //從堆裡取，放進數組裡        for (int i = 0; i < 100; i++) {            arr[i] = maxHeap.popMax();            System.out.print(arr[i] + " ");        }        System.out.println();    }}

　　

最大堆(Java數組實現)