java数据结构总结——堆

（一）自己实现一个大根堆

import java.util.Arrays;

public class TestHeap {
    public int[] elem;
    public int usedSize;
    public TestHeap() {
        this.elem = new int[10];
    }
    //向下调整
    public void adjustDown(int root,int len) {
         int parent = root;
         int child = 2*parent + 1;
         while(child < len) {
             if(child+1 < len && this.elem[child+1] > this.elem[child]) {
                 child++;
             }
             if(this.elem[child] > this.elem[parent]) {
                 int tmp = this.elem[child];
                 this.elem[child] = this.elem[parent];
                 this.elem[parent] = tmp;
                 parent = child;
                 child = 2*parent + 1;
             } else {
                 break;
             }
         }
    }
    //向上调整
    public void adjustUp(int child) {
        int parent = (child -1) /2;
        while(child > 0) {
            if(this.elem[parent] < this.elem[child]) {
                int tmp = this.elem[parent];
                this.elem[parent] = this.elem[child];
                this.elem[child] = tmp;
                child = parent;
                parent = (child -1) /2;
            } else {
                break;
            }
        }
    }
   //创建堆
    public void createHeap(int[] array) {
        for (int i = 0; i < array.length ; i++) {
            this.elem[i] = array[i];
            this.usedSize++;
        }
        for (int i = (this.usedSize-2)/2; i >= 0 ; i--) {
            adjustDown(i,this.usedSize);
        }

    }
    //添加一个元素
    public void push(int val) {
        if(isFull()) {
            this.elem = Arrays.copyOf(this.elem,this.elem.length*2);
        }
        this.elem[this.usedSize] = val;
        this.usedSize++;
        adjustUp(this.usedSize-1);

    }
   //删除一个元素
    public void pop() {
        if(isEmpty()) {
            return;
        }
        int tmp = this.elem[0];
        this.elem[0] = this.elem[this.usedSize-1];
        this.elem[this.usedSize-1] = tmp;
        this.usedSize--;
        adjustDown(0,this.usedSize);
    }
    //拿到堆顶元素
    public int peek() {
        if(isEmpty()) {
            return -1;
        }
        return this.elem[0];
    }
    //用堆实现升序排序
    public void heapSort() {
        int end = this.usedSize-1;
        while(end > 0) {
            int tmp = this.elem[0];
            this.elem[0] = this.elem[end];
            this.elem[end] = tmp;
            adjustDown(0,end);
            end--;
        }
    }
    public boolean isEmpty() {
        return this.usedSize == 0;
    }
    public boolean isFull() {
        return this.usedSize == this.elem.length;
    }
    public void show() {
        for (int i = 0; i < this.usedSize ; i++) {
            System.out.print(this.elem[i] +" ");
        }
        System.out.println();
    }

}