2. 判断二叉树是否相等

解题思路：用栈(stack)模拟实现

/**
 * struct TreeNode {
 *	int val;
 *	struct TreeNode *left;
 *	struct TreeNode *right;
 * };
 */

class Solution {
public:
    /**
     * 
     * @param p TreeNode类 
     * @param q TreeNode类 
     * @return bool布尔型
     */
    bool isSameTree(TreeNode* p, TreeNode* q) {
        // write code here
        if (p == nullptr || q == nullptr)
        {
            return p == q;
        }
        stack<TreeNode*> st1, st2;
        st1.push(p);
        st2.push(q);
        while (!st1.empty() && !st2.empty())
        {
            TreeNode* a = st1.top();
            TreeNode* b = st2.top();
            st1.pop();
            st2.pop();
            if (a->val != b->val)
            {
                return false;
            }
            if (a->left && b->left)
            {
                st1.push(a->left);
                st2.push(b->left);
            }
            else if (a->left || b->left)
            {
                return false;
            }
            if (b->right && b->right)
            {
                st1.push(a->right);
                st2.push(b->right);
            }
            else if (b->right || b->right)
            {
                return false;
            }
        }
        if (st1.empty() && st2.empty())
        {
            return true;
        }
        else
        {
            return true;
        }
        
    }
};