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;        }    }};