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.

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递归方法：

/** * Definition for a binary tree node. * 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) {        //递归主要是推出条件的判断，，写好推出条件就行        if(p==NULL && q==NULL)            return true;        else if(p==NULL && q!=NULL)            return false;        else if(p!=NULL && q==NULL)            return false;        else        {            if(p->val != q->val)                return false;            else                return isSameTree(p->left, q->left) && isSameTree(p->right, q->right);        }    }};

  非递归方法

/** * Definition for a binary tree node. * 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) {       //非递归的方法，主要判断各个元素是不是相同，就是三种遍历方法,因为从上到下进行遍历，最好是层次遍历       queue<TreeNode*> a1;       queue<TreeNode*> a2;       if(p==NULL && q==NULL) return true;       if((p && !q)||(!p && q)||(p->val!=q->val)) return false;       a1.push(p);       a2.push(q);       while(!a1.empty() && !a2.empty())       {           TreeNode* p1=a1.front();           a1.pop();           TreeNode* p2=a2.front();           a2.pop();           //一个重要的是NULL左右子树也得放进去 保持同步，如果是NULL,则他的左右子树不用放进去           if(p1==nullptr && p2==nullptr) continue;              if(p1==nullptr || p2==nullptr) return false;                            if( p1->val != p2->val) return false;                            a1.push(p1->left);              a1.push(p1->right);              a2.push(p2->left);              a2.push(p2->right);                          }              return true;    }};