Same Tree 比較兩個二叉樹是否完全相同

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.

給定兩個二叉樹，判斷是否完全相同。

若兩個二叉樹完全相同，則每個節點的左子樹和右子樹必然都相同。

可以採用遞迴方式，從根節點開始：

/**
 * 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) {
        if(p == NULL && q == NULL)
            return true;
        else if(p == NULL || q == NULL)
            return false;
        
        if(p->val != q->val)
            return false;
        
        bool left = isSameTree(p->left,q->left);
        bool right = isSameTree(p->right,q->right);
        
        return left && right;
    }
};