# Leetcode : 0100. Same Tree (Tree)
###### tags:`leetcode`

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
public:
    bool isSameTree(TreeNode* p, TreeNode* q) {
        
        if(p==nullptr && q==nullptr) return true;  //p and q two is null
        if(p==nullptr || q==nullptr) return false; //p or q one is null.
        if(p->val != q->val) return false;

        return isSameTree(p->left,q->left) && isSameTree(p->right,q->right);
    }
};

//how do true type
//last node ,nullptr == nullptr

//how do false type
//1.val != nullptr 
//2.val != val

> Tip
> how condsider how true type and false type.