題目：

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. 

思路：

遞迴判斷左子樹和右子樹的值相不相等就行。

程式碼：

/**
 * 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) {
        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);
    }
}