void push_down(int pos)
{
    if(tree[pos].x==1)
    {
        tree[left].mx=tree[pos].lazy1+tree[pos].lazy2;//一定要加上lazy2
        tree[right].mx=tree[pos].lazy1+tree[pos].lazy2;
        tree[left].lazy1=tree[pos].lazy1,tree[left].x=1;
        tree[right].lazy1=tree[pos].lazy1,tree[right].x=1;
        tree[left].lazy2=tree[pos].lazy2;//很重要
    	tree[right].lazy2=tree[pos].lazy2;//很重要
	}
	else if(tree[pos].lazy2!=0)
	{
		tree[left].mx+=tree[pos].lazy2;
    	tree[right].mx+=tree[pos].lazy2;
    	tree[left].lazy2+=tree[pos].lazy2;
    	tree[right].lazy2+=tree[pos].lazy2;
	}        
	tree[pos].lazy1=0,tree[pos].x=0;
	tree[pos].lazy2=0;
}

不然会错的很惨 （ 超小声）