[LC 116.填充每个节点的下一个右侧节点指针]

递归调用

/*
// 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 null;
        connectTwoNode(root.left,root.right);
        return root;

    }
    public void connectTwoNode(Node a,Node b){
        if (a == null || b == null )
            return ;
        a.next = b;
        connectTwoNode(a.left,a.right);
        connectTwoNode(a.right,b.left);
        connectTwoNode(b.left,b.right);
    }
}