二叉树相关算法

1. 二叉树最低公共父节点

struct TreeNode {
	int val;
	TreeNode *left;
	TreeNode *right;
	TreeNode(int x) : val(x), left(NULL), right(NULL) {}
};

TreeNode* lowestCommonAncestor(TreeNode* root, TreeNode* p, TreeNode* q) {
	if (!root) return NULL;
	if (root == p || root == q) return root;
	TreeNode* left = lowestCommonAncestor(root->left, p, q);
	TreeNode* right = lowestCommonAncestor(root->right, p, q);
	if (left && right) return root;
	else if (!left && right) return right;
	else if (left && !right) return left;
	else return NULL;
}

2. 对称二叉树

bool func(TreeNode* pLeft, TreeNode* pRight);

bool isSymmetrical(TreeNode* root)
{
	if (!root) return true;
	return func(root->left, root->right);
}

bool func(TreeNode* pLeft, TreeNode* pRight) 
{
	if (!pLeft && !pRight) return true;
	if (pLeft && !pRight || !pLeft && pRight) return false;
	if (pLeft->val != pRight->val) return false;
	return func(pLeft->left, pRight->right) && func(pLeft->right, pRight->left);
}

3. 层序打印二叉树

vector<vector<int> > print(TreeNode* pRoot) 
{
	vector<vector<int> > res;
	if (!pRoot) return res;
	queue<TreeNode*> que1;
	queue<TreeNode*> que2;
	queue<TreeNode*>* p1 = &que1;
	queue<TreeNode*>* p2 = &que2;
	p1->push(pRoot);
	vector<int> vec;
	while (!p1->empty()) 
	{
		TreeNode* temp = p1->front();
		p1->pop();
		if (temp->left) p2->push(temp->left);
		if (temp->right) p2->push(temp->right);
		vec.push_back(temp->val);
		if (p1->empty()) 
		{
			res.push_back(vec);
			vec.clear();
			queue<TreeNode*>* p = p1;
			p1 = p2;
			p2 = p;
		}
	}
	return res;
}