Populating Next Right Pointers in Each Node和 II

二叉树层次遍历的变种

用辅助队列，一层一层地遍历每一层的元素，先出队的元素的next是后一个出队的元素

每一层最后一个元素的next=null

II的解法也一样

public void connect(TreeLinkNode root) {
        Queue<TreeLinkNode> Q = new ArrayDeque<TreeLinkNode>();
        if(root == null)return;
        Q.offer(root);
        int count = 1;
        while(!Q.isEmpty()){
            int nextCount = 0;
            for(int i =0;i<count;i++){
                TreeLinkNode p = Q.poll();
                if(p.left != null){
                    Q.offer(p.left);
                    nextCount++;
                }
                if(p.right != null){
                    Q.offer(p.right);
                    nextCount++;
                }
                TreeLinkNode q = null;
                if(i < count-1)q = Q.peek();
                p.next = q;
            }
            count = nextCount;
        }
    }