【3对1错2】Merge Two Binary Trees

https://leetcode.com/problems/merge-two-binary-trees/

日期	是否一次通过	comment
2018-12-10 22:08	递归一次；遍历两次	印象不深，遍历仍旧在机械记忆
2018-12-11 21:09	一次通过	有点晕，直接机械记忆
2018-12-12 20:40	一次通过	机械记忆
2018-12-21 17:18	一次通过，但印象不深	摸索着写完的，脑子里感觉和其他题有点类似

image.png

（来源：https://leetcode.com/problems/merge-two-binary-trees/）

递归

class Solution {
    public TreeNode mergeTrees(TreeNode t1, TreeNode t2) {
        if(t1 == null) {
            return t2;
        }
        if(t2 == null) {
            return t1;
        }
        
        t1.val +=  t2.val;
        
        t1.left = mergeTrees(t1.left, t2.left);
        t1.right = mergeTrees(t1.right, t2.right);
        
        return t1;
    }
}

遍历

class Solution {
    public TreeNode mergeTrees(TreeNode t1, TreeNode t2) {
        if(t1 == null) {
            return t2;
        }
        
        Queue<TreeNode[]> nodeQ = new LinkedList<>();
        nodeQ.offer(new TreeNode[]{t1, t2});
        while(!nodeQ.isEmpty()) {
            TreeNode[] nodeArray = nodeQ.poll();
            if(nodeArray[0] == null || nodeArray[1] == null) {
                continue;
            }
            nodeArray[0].val += nodeArray[1].val;
            
            if(nodeArray[0].left == null) {
                nodeArray[0].left = nodeArray[1].left;
            } else {
                nodeQ.offer(new TreeNode[]{nodeArray[0].left, nodeArray[1].left});
            }
            
            if(nodeArray[0].right == null) {
                nodeArray[0].right = nodeArray[1].right;
            } else {
                nodeQ.offer(new TreeNode[]{nodeArray[0].right, nodeArray[1].right});
            }
        }
        
        return t1;
    }
}