小编点评

```python class TreeNode: def __init__(self, val): self.val = val self.left = None self.right = None def isSameTree(p, q): # Base Case 1: Two trees are empty if p is None and q is None: return True # Base Case 2: One of the trees is null if p is None or q is None: return False # Check the values of the two nodes if p.val != q.val: return False # Recursively check the left and right subtrees return isSameTree(p.left, q.left) and isSameTree(p.right, q.right) ``` **Explanation:** * The `isSameTree` function takes two binary trees, `p` and `q`, as input. * It checks if the two trees are empty. If they are, it returns `True` since two empty trees are considered identical. * If one of the trees is null, it returns `False` since the other tree cannot be a duplicate. * It checks if the two nodes have the same value. If they do not, it returns `False`. * It recursively checks the left and right subtrees of `p` and `q` to ensure they are the same. * If both subtrees are valid and have the same structure, it returns `True`. * Otherwise, it returns `False`. **Example Usage:** ```python # Example 1: p = TreeNode(1) q = TreeNode(1) print(isSameTree(p, q)) # Output: True # Example 2: p = TreeNode(1) q = TreeNode(1, TreeNode(null), TreeNode(null)) print(isSameTree(p, q)) # Output: False # Example 3: p = TreeNode(1) q = TreeNode(1, TreeNode(1), TreeNode(2)) print(isSameTree(p, q)) # Output: False ```

正文

给你两棵二叉树的根节点 p 和 q ，编写一个函数来检验这两棵树是否相同。

如果两个树在结构上相同，并且节点具有相同的值，则认为它们是相同的。

示例 1：

输入：p = [1,2,3], q = [1,2,3]
输出：true
示例 2：

输入：p = [1,2], q = [1,null,2]
输出：false
示例 3：

输入：p = [1,2,1], q = [1,1,2]
输出：false

解法思路

0. 如果进来的两个节点都是null，那么相同
1. 如果进来的两个树就只有自己一个节点，那么只要判断自己是否相同就可以了
2. 如果进来的两个树当前节点值相同，则判断他两的子树是否相同（这里利用递归的思想）

/**
 * 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 boolean isSameTree(TreeNode p, TreeNode q) {
        if (p == null && q == null) {
            return true;
        }

        if (p == null || q == null) {
            return false;
        }

        if (p.val != q.val) {
            return false;
        }

        return isSameTree(p.left, q.left) && isSameTree(p.right, q.right);
    }
}