题目如下：

Given two binary trees, write a function to check if they are the same or not.
Two binary trees are considered the same if they are structurally identical and the nodes have the same value.

LeetCode-100 Same Tree
给定两个二叉树，让我们判断两棵二叉树是否完全相同。只需按序遍历每一个二叉树节点即可，判断节点的值是否相等，注意递归的返回条件即可。
代码如下：

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 * int val;
 * TreeNode left;
 * TreeNode right;
 * TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    public boolean isSameTree(TreeNode p, TreeNode q) {
        if (p == null) {
            return q == null;
        }
        if (q == null) {
            return p == null;
        }
        if (p.val != q.val) {
            return false;
        }
        boolean left = isSameTree(p.left, q.left);
        boolean right = isSameTree(p.right, q.right);
        return left == true && right == true;
    }
}

时间复杂度和空间复杂度均为O（n）。