100. Same Tree和判断一个树是不是对称的思想一样

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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1.递归的代码

bool isSameTree(TreeNode* p, TreeNode* q) {
if(p == NULL && q == NULL)
return true;
else if(p == NULL || q == NULL)
return false;

if(p->val != q->val)
return false;
return isSameTree(p->left,q->left)&&isSameTree(p->right,q->right);
}

更简洁的递归代码：

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));
}

2.非递归的代码

bool isSameTree(TreeNode* p, TreeNode* q) {
if(p == NULL && q == NULL)
return true;
else if(p == NULL || q == NULL)
return false;

queue<TreeNode*> quep;
queue<TreeNode*> queq;

quep.push(p);
queq.push(q);
while(!quep.empty() && !queq.empty())
{
TreeNode* tempp = quep.front();
TreeNode* tempq = queq.front();
quep.pop();
queq.pop();
if(tempp->val != tempq->val)
{

return false;
}
if(tempp->left != NULL && tempq->left != NULL)
{
quep.push(tempp->left);
queq.push(tempq->left);
}
else if((tempp->left == NULL && tempq->left != NULL) || (tempp->left != NULL && tempq->left == NULL))
return false;

if(tempp->right != NULL && tempq->right != NULL)
{
quep.push(tempp->right);
queq.push(tempq->right);
}
else if((tempp->right == NULL && tempq->right != NULL) || (tempp->right != NULL && tempq->right == NULL))
return false;
}

if(!quep.empty() || !queq.empty())
return false;
return true;
}

更简洁的代码：

bool isSameTree(TreeNode* p, TreeNode* q) {
if(p == NULL && q == NULL)
return true;
else if(p == NULL || q == NULL)
return false;

queue<TreeNode*> quep;
queue<TreeNode*> queq;

quep.push(p);
queq.push(q);
while(!quep.empty() && !queq.empty())
{
TreeNode* tempp = quep.front();
TreeNode* tempq = queq.front();
quep.pop();
queq.pop();
if(tempp->val != tempq->val)
return false;

if(tempp->left != NULL)
quep.push(tempp->left);
if (tempq->left != NULL)
queq.push(tempq->left);
if(quep.size() != queq.size())
return false;

if(tempp->right != NULL)
quep.push(tempp->right);
if(tempq->right != NULL)
queq.push(tempq->right);
if(quep.size() != queq.size())
return false;
}

if(!quep.empty() || !queq.empty())
return false;
return true;
}