java">class MedianFinder {//A为小根堆，B为大根堆List<Integer> A,B;public MedianFinder() {A = new ArrayList<Integer>();B = new ArrayList<Integer>();}public void addNum(int num) {int m = A.size(),n = B.size();if(m == n){insert(B,num);int top = deleteTop(B);insert(A,top);}else{insert(A,num);int top = deleteTop(A);insert(B,top);}}//删除堆顶元素并返回其值private int deleteTop(List<Integer> list){Collections.swap(list,0,list.size() - 1);int heapSize = list.size() - 1;int root = 0;while(root < heapSize/2){int left = root * 2 + 1,right = root * 2 + 2,largest = root;if(left < heapSize && comparee(list,left,largest))largest = left;if(right < heapSize &&  comparee(list,right,largest))largest = right;if(root == largest)break;Collections.swap(list,root,largest);root = largest;}return list.remove(list.size() - 1);}//A小根堆的比较方法：比较值<目标值？private boolean comparee(List<Integer> list,int source,int target){if(list == A)return list.get(source) < list.get(target);elsereturn list.get(source) > list.get(target);}//将数插入到堆中private void insert(List<Integer> list,int num){list.add(num);int index = list.size() - 1;while(index > 0){int root = (index - 1) / 2;if(!comparee(list,index,root))break;Collections.swap(list,root,index);index = root;}}public double findMedian() {int m = A.size(),n = B.size();return (m==n) ? (A.get(0) + B.get(0)) / 2.0 : A.get(0);}
}