1、問題描述

Given two binary trees, write a function to check if they are equal or not.

Two binary trees are considered equal if they are structurally identical and the nodes have the same value.

2、邊界條件：無

3、思路：遞歸，兩顆數is same的條件是val相等，子樹也是same。但是判斷val的前提條件是有val，即不為null。

base case：兩顆數都為空；一顆為空，一顆不為空。

4、代碼實現

/**
 * 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 && q == null) {//base case是兩個節點都為空
            
 
return true;
        }
        if (p == null || q == null) {
            return false;
        }
        return p.val == q.val
               && isSameTree(p.left, q.left)
               && isSameTree(p.right, q.right);
    }
}

leetcode-- 100. Same Tree