leetcode 1046

class Solution {
   
    public int lastStoneWeight(int[] stones) {
        MaxHeap s=new MaxHeap(stones.length+1);
        for(int i=0;i<stones.length;i++)
        {
            s.insert(stones[i]);
        }
        while(s.size()>1)
        {
            int y=s.extractMax();
            int x=s.extractMax();
            if(y>x)
            {
                s.insert(y-x);
            }
        }
        if(s.size()==1)
        {
            return s.extractMax();
        }
        else
            return 0;
        
    }
}
class MaxHeap{
    private int[] stone;
    private int count;
    private int capacity;
    public MaxHeap(int capacity)
    {
        this.capacity=capacity;
        stone=new int[capacity+1];
        count=0;
    }
    public void insert(int n)
    {
        stone[++count]=n;
        shiftUp(count);
    }
    private void shiftUp(int count)
    {
        while(count>1&&stone[count/2]<stone[count])
        {
            swap(count/2,count);
            count=count/2;
        }
    }
    public void swap(int i,int j)
    {
        int temp=stone[i];
        stone[i]=stone[j];
        stone[j]=temp;
    }
    public int extractMax()
    {
        int res=stone[1];
        swap(1,count);
        count--;
        shiftDown(1);
        return res;
    }
    private void shiftDown(int i)
    {
      int j=2*i;
      while(j<=count)
      {
          if(j+1<=count&&stone[j+1]>stone[j])
          {
              if(stone[j+1]>stone[i])
              {
                   swap(j+1,i);
                   i=j+1;
                   j=2*i;
              }
              else
                  break;
             
          }
          else
          {
              if(stone[j]>stone[i])
              {
                  swap(j,i);
                  i=j;
                  j=2*i;
              }
              else
                  break;
          }
      }
    }  
    public int size()
    {
        return count;
    }
}