Find All the Lonely Nodes

给一个二叉树, 定一个lonely node是一个node只有一个child, 返回这些child. 用层序扫描即可.

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    public List<Integer> getLonelyNodes(TreeNode root) {
        Queue<TreeNode> q = new LinkedList<>();
        q.add(root);
        List<Integer> res = new ArrayList<>();
        while(!q.isEmpty()) {
            int size = q.size();
            for(int i = 0; i < size; i++) {
                TreeNode node = q.poll();
                if(node.left != null && node.right == null)
                {
                    res.add(node.left.val);
                }
                if(node.left == null && node.right != null)
                {
                    res.add(node.right.val);
                }
                if(node.left != null) {
                    q.add(node.left);
                }
                if(node.right != null) {
                    q.add(node.right);
                }
            }
        }
        return res;
    }
}