找出两个整型数组中的公共元素的最大值

//给定两个整形数组,寻找这两个数组的公有的且最大的元素
public class MaxCommonEle {

    public static int findCommMax(int[] arr1, int[] arr2)
    {
        if(arr1 == null || arr2 == null)
            throw new NullPointerException();
        if(arr1.length == 0 || arr2.length == 0)
            throw new IllegalArgumentException();
        
        //build heap--大顶堆 , time complex: O(M)
            for(int i = arr1.length / 2 -1; i >= 0; i--)
                percDown(arr1, i, arr1.length);
            
        //build heap, O(N)
        for(int i = arr2.length / 2 - 1; i >= 0; i--)
            percDown(arr2, i, arr2.length);
        
        int len_1 = arr1.length - 1;
        int len_2 = arr2.length - 1;
        while(len_1 >= 0 && len_2 >=0)
        {
            int max1 = arr1[0];//获取大顶堆的根元素,即数组中的最大值
            int max2 = arr2[0];
            
            if(max1 > max2)//如果arr1的堆顶元素要大,则删除arr1的堆顶元素
            {
                swap(arr1, 0, len_1);//delete arr1‘s root
                percDown(arr1, 0, len_1);//进行堆调整, 删除了最后一个元素,刚好堆调整的元素个数为 len_1
                len_1--;
            }
            else if( max1 //如果arr2的堆顶元素要大,则删除arr2的堆顶元素
            {
                swap(arr2, 0, len_2);
                percDown(arr2, 0, len_2);
                len_2--;
            }
            else//arr1的堆顶元素与 arr2的堆顶元素相等了.
                return max1;
        }
        return -1;// -1 means there are no common element
    }
    
    private static void percDown(int[] arr, int i, int n)
    {
        int tmp;
        int child;
        
//        int k = leftChild(i);
        for(tmp = arr[i]; leftChild(i)  child)
        {
            child = leftChild(i);
            
            if(child != n-1 && arr[child] ])
                child = child + 1;
            if(tmp < arr[child])
                arr[i] = arr[child];
            else
                break;
        }
        arr[i] = tmp;
    }
    
    private static int leftChild(int i){
        return (i <<1 ) + 1;
    }
    
    private static void swap(int[] arr ,int i, int j)
    {
        int tmp = arr[i];
        arr[i] = arr[j];
        arr[j] = tmp;
    }
    
    
    //hapjin test
    public static void main(String[] args) {
        int[] arr1 = {8,2,9,6,18,7,25,28};
        int[] arr2 = {6,39,4,9,25,18,36,12};
        
//        int[] arr1 = {4,2,8};
//        int[] arr2 = {10,4,6};

//        int[] arr1 = {4,2,8};
//        int[] arr2 = {5,7,9};
        int res = findCommMax(arr1, arr2);
        System.out.println(res);
    }
}