Leetcode - Tree - 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.

Recursive Solution

/**
 * 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) { // 时间复杂度O(n)，平均空间复杂度O(sqrt(n))，BinarySearch Tree空间复杂度为O(lgn)
        if(p==NULL&&q==NULL)
            return true;
        if(p==NULL&&q!=NULL||p!=NULL&&q==NULL)
            return false;
        if(p->val==q->val&&isSameTree(p->left,q->left)&&isSameTree(p->right,q->right))
            return true;
        else
            return false;
    }
};

iterative Solution

/**
 * 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) {
        // 时间复杂度为O(n),平均空间复杂度为O(sqrt(n))
        stack<TreeNode*> treeStack;
        treeStack.push(p);
        treeStack.push(q);
        while(!treeStack.empty()&&!treeStack.empty())
        {
            p=treeStack.top();
            treeStack.pop();
            q=treeStack.top();
            treeStack.pop();
            if(p==NULL&&q==NULL)
                continue;
            if(p&&q&&p->val==q->val)
            {
                treeStack.push(p->left);
                treeStack.push(q->left);
                treeStack.push(p->right);
                treeStack.push(q->right);
            }
            else
                return false;
        }
    }
};