100.Same Tree

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.

//递归的版本
class Solution {
public:
    bool isSameTree(TreeNode* p, TreeNode* q) {
        if(p == NULL || q == NULL) return p == q;
        return p->val == q->val && isSameTree(p->left, q->left) && isSameTree(p->right, q->right);
    }
};

//迭代的版本
class Solution {
public:
    bool isSameTree(TreeNode* p, TreeNode* q) {
        stack<TreeNode*> stack_p;
        stack<TreeNode*> stack_q;
        if(p)   stack_p.push(p);
        if(q)   stack_q.push(q);
        while(!stack_p.empty() && !stack_q.empty()){
            TreeNode* cur_p=stack_p.top();
            TreeNode* cur_q=stack_q.top();
            stack_p.pop();
            stack_q.pop();
            if(cur_p->val != cur_q->val) return false;
            if(cur_p->left) stack_p.push(cur_p->left);
            if(cur_q->left) stack_q.push(cur_q->left);

            if(stack_p.size() != stack_q.size())    return false;
            if(cur_p->right) stack_p.push(cur_p->right);
            if(cur_q->right) stack_q.push(cur_q->right);
            if(stack_p.size() != stack_q.size())    return false;
        }
        return stack_p.size() == stack_q.size();
    }
};