1.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.題目要求：判斷兩個二叉樹是否相等。

3.方法：檢查當(dāng)前節(jié)點的左右節(jié)點是否相同，然后遞歸檢查左子樹和右子樹。

4.代碼：
/**

• Definition for binary tree
• struct TreeNode {

• int val;
  

• TreeNode *left;
  

• TreeNode *right;
  

• TreeNode(int x) : val(x), left(NULL), right(NULL) {}
  

• };
  */
  class Solution {
  public:
  bool isSameTree(TreeNode *p, TreeNode *q) {
  // Start typing your C/C++ solution below
  // DO NOT write int main() function
  if (p == NULL && q == NULL)
  return true;
  else if (p == NULL || q == NULL)
  return false;
  return p->val == q->val && isSameTree(p->left, q->left)
  && isSameTree(p->right, q->right);
  }
  };