leetcode[Merge Two Binary Trees]

/**
* Definition for a binary tree node.
* public class TreeNode {
*     int val;
*     TreeNode left;
*     TreeNode right;
*     TreeNode(int x) { val = x; }
* }
*/
class Solution {
public TreeNode mergeTrees(TreeNode t1, TreeNode t2) {
TreeNode root = null;
if(t1 == null && t2 == null){
return root;
}
int val = (t1 == null ? 0 : t1.val) + (t2 == null ? 0 : t2.val);
root = new TreeNode(val);
//递归就是根据宏观的，处理根节点的左右子树（子节点）
root.left = mergeTrees(t1 == null ? null : t1.left, t2 == null ? null : t2.left);
root.right = mergeTrees(t1 == null ? null : t1.right, t2 == null ? null : t2.right);

//宏观，整棵树的左右子树，根节点都处理完了，就返回根节点
return root;
}
}