1 class Solution { 2     public void connect(TreeLinkNode root) { 3         if(root == null) return; 4         Queue
     
       queue = new LinkedList<>(); 5         queue.offer(root); 6         int size = queue.size(); 7         while(!queue.isEmpty()) { 8             TreeLinkNode prev = null; 9             for(int i = 0; i < size; i++) {10                 TreeLinkNode node = queue.poll();11                 if(node.left != null) {  //注意不是空的再加进去 别忘了12                     queue.offer(node.left);13                 }14                 if(node.right != null) {15                     queue.offer(node.right);16                 }17                 if(i == 0) {18                     prev = node;19                 }else{20                     prev.next = node;21                     prev = node;22                 }23                 if(i == size - 1) {24                     node.next = null;25                 }26             }27             size = queue.size();28         }29     }30 }