快乐的LeetCode --- 相同的树

ゝ一世哀愁。 2023-03-14 08:29 8阅读 0赞

**题目描述：**

给定两个二叉树，编写一个函数来检验它们是否相同。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:       1         1
              / \       / \
             2   3     2   3
    
            [1,2,3],   [1,2,3]
    
    输出: true

**示例 2:**

输入:      1          1
              /           \
             2             2
    
            [1,2],     [1,null,2]
    
    输出: false

**示例 3:**

输入:       1         1
              / \       / \
             2   1     1   2
    
            [1,2,1],   [1,1,2]
    
    输出: false

--------------------

**解题思路1:**

二叉树的前序遍历与题目中描述的顺序一致，但是目前受限于判断 `[1,2]` 和 `[1,null,2]`。

--------------------

**代码1：**

class Solution(object):
        def isSameTree(self, p, q):
            if p is not None and q is not None:
                return True
            stack1, output1 = [p], []
            stack2, output2 = [q], []         
             
            while  stack1:
                root1 = stack1.pop()
                if root1 is not None:
                    output1.append(root1)
                    if root1.right is not None:
                        stack1.append(root1.right)
                    else:
                        stack1.append(null)
                    if root1.left is not None:
                        stack1.append(root1.left)
                    else:
                        stack1.append(null)
            
            while  stack2:
                root2 = stack2.pop()
                if root2 is not None:
                    output2.append(root2)
                    if root2.right is not None:
                        output2.append(root2.right)
                    else:
                        stack2.append(null)
                    if root2.left is not None:
                        output2.append(root2.left)
                    else:
                        stack2.append(null)
    
            if output1 == output2:
                return True
            return False

--------------------

**解题思路2:**

递归思路

--------------------

**代码2：**

# Definition for a binary tree node.
    # class TreeNode(object):
    #     def __init__(self, x):
    #         self.val = x
    #         self.left = None
    #         self.right = None
    
    class Solution(object):
        def isSameTree(self, p, q):
            if not p and not q:
                return True
            if not p or not q:
                return False
    
            if p.val != q.val:   # 这里的写法不能是当二者相等就返回True，因为我们还需要判断接下来的情况
                return False
    
            return self.isSameTree(p.left, q.left) and self.isSameTree(p.right, q.right)

--------------------

**题目来源：**

[https://leetcode-cn.com/problems/same-tree][https_leetcode-cn.com_problems_same-tree]

[https_leetcode-cn.com_problems_same-tree]: https://leetcode-cn.com/problems/same-tree