LeetCode100 相同的树

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
/*
算法思想：
    采用递归，递归比较两棵树即可。
*/
class Solution {
public:
    bool isSameTree(TreeNode* p, TreeNode* q) {
        if(!p && !q)
            return true;
        if((!p&&q)||(p&&!q)||(p->val!=q->val))
            return false;
        return isSameTree(p->left,q->left)&&isSameTree(p->right,q->right);
    }
};
/*
算法思想：
    采用迭代，利用栈保存结点然后比较结点即可。
*/
class Solution {
public:
    bool isSameTree(TreeNode* p, TreeNode* q) {
        stack<TreeNode*> s1, s2;
        if (p)  s1.push(p);
        if (q)  s2.push(q);
        while (!s1.empty() && !s2.empty()) {
            TreeNode *t1 = s1.top(); s1.pop();  //这是关键，先取在弹栈
            TreeNode *t2 = s2.top(); s2.pop();
            if (t1->val != t2->val) 
                return false;
            
            if (t1->left) s1.push(t1->left);
            if (t2->left) s2.push(t2->left);
            if (s1.size() != s2.size()) 
                return false;
            
            if (t1->right) s1.push(t1->right);
            if (t2->right) s2.push(t2->right);
            if (s1.size() != s2.size()) 
                return false;
        }
        return s1.size() == s2.size();
    }
};