力扣116

算中序吧

/*
// Definition for a Node.
class Node {
    public int val;
    public Node left;
    public Node right;
    public Node next;
    public Node() {}
    public Node(int _val) {
        val = _val;
    }
    public Node(int _val, Node _left, Node _right, Node _next) {
        val = _val;
        left = _left;
        right = _right;
        next = _next;
    }
};
*/
class Solution {
    public Node connect(Node root) {
        if (root == null){
            return root;
        }
        //逐层进队
        Queue<Node> level = new LinkedList<Node>();//这里括号别漏了
        level.add(root);//此时第一层进来
        while(!level.isEmpty()){
            int num = level.size();//这里如果不这样 后面使用level.size()是变化的 就会出错
            for(int i = 0; i < num; ++i){
                Node node = level.poll();
                if (i < num-1){
                    node.next = level.peek();
                }
                //一种类似中序的
                if (node.left != null){
                    level.add(node.left);
                }
                if (node.right != null){
                    level.add(node.right);
                }
            }
        }
        return root;
    }
}