题目链接

层序遍历

/**
 * 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 TreeNode mergeTrees(TreeNode root1, TreeNode root2) {
        if(root1 == null){
            return root2;
        }
        if(root2 == null){
            return root1;
        }
        Deque<TreeNode> queue = new LinkedList<TreeNode>();
        queue.offer(root1);
        queue.offer(root2);
        while(!queue.isEmpty()){
            TreeNode node1 = queue.poll();
            TreeNode node2 = queue.poll();
            node1.val += node2.val;
            if(node1.left != null && node2.left != null){
                queue.offer(node1.left);
                queue.offer(node2.left);
            }
            if(node1.right != null && node2.right != null){
                queue.offer(node1.right);
                queue.offer(node2.right);
            }
            if(node1.left == null && node2.left != null){
                node1.left = node2.left;
            }
            if(node1.right == null && node2.right != null){
                node1.right = node2.right;
            }
        }
        return root1;
    }
}