題目說明:給定兩棵樹，要判斷兩棵樹是否相等

Case 1

Input: p = [1,2,3], q = [1,2,3]
Output: true

Case 2

Input: p = [1,2], q = [1,null,2]
Output: false

Case 3

Input: p = [1,2,1], q = [1,1,2]
Output: false

要判斷兩棵樹是否相同，我們需要考慮兩個情況:

1. 是否都為空值(null)
2. 兩者的值都相同

附上程式碼以及註解

Java

/**
 * 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;//兩棵樹都為空值(null)就回傳true
        if (q == null || p == null) return false;//其中之一為空值(null)回傳false
        if (p.val != q.val) return false;//若兩者的值不相同就回傳false
        return isSameTree(p.left,q.left)&&isSameTree(p.right,q.right);
        //用遞迴的方式重複檢查兩棵樹的左右子樹是否相同
    }
}

Python

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution:
    def isSameTree(self, p: Optional[TreeNode], q: Optional[TreeNode]) -> bool:
        if not p and not q:
            return True     #兩棵樹都為空值(None)就回傳true
        if not q or not p:
            return False    #其中之一為空值(None)回傳false
        if p.val != q.val:
            return False    #若兩者的值不相同就回傳false
        return self.isSameTree(p.right, q.right) and self.isSameTree(p.left, q.left)
        #用遞迴的方式重複檢查兩棵樹的左右子樹是否相同