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;}