拙劣算法：堆建立

说明

某一个节点i父节点，子节点公式：
父节点=（i -1）/2
左子节点=2i+1
右子节点=2i+1

heapify用于就某一个i节点搞堆，用到递归，如果存在交换，被交换的点要递归搞堆。

buildHeap用来建立堆，怎么建立的呢，从最后一个节点往上执行heapify操作。想想为什么要这样做？？因为从下往上，可以确保下面的先搞成堆，上面的就可以用下面的了。

        int[] arr = {4,10,3,5,1,2,100};
        int[] heap = buildHeap(arr,7);
        for (int i = 0; i < heap.length; i++) {
            Log.i("findnum"," " + heap[i]);
       }


    private int[] heapify(int [] tree, int size,int i) {
        int left = 2 * i + 1;
        int right = 2 * i + 2;
        if (right > size -1 || left > size -1) {
            return tree;
        }
        int max = i;
        if (tree[left] > tree[i]) {
            max = left;
        }
        if (tree[right] > tree[i]) {
            max = right;
        }
        if (max != i) {
            int temp = tree[i];
            tree[i] = tree[max];
            tree[max] = temp;
            return heapify(tree, size, max);
        }
        return tree;
    }

    private int[] buildHeap(int [] tree, int size) {
        int round = 1;
        for (int i = size -1; i >= 0 ; i--) {
            Log.i("findnum","rount :" + round + "try heap:" + tree[i]);
            tree = heapify(tree,size,i);
            for (int j = 0; j < tree.length; j++) {
                Log.i("findnum"," " + tree[j]);
            }
            round++;
        }
        return tree;
    }

参考：https://www.bilibili.com/video/av47196993/?redirectFrom=h5