題目為：

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.

程式碼為：

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