树02

226. 翻转二叉树

/*** Definition for a binary tree node.* struct TreeNode {*     int val;*     TreeNode *left;*     TreeNode *right;*     TreeNode() : val(0), left(nullptr), right(nullptr) {}*     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}*     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}* };*/
class Solution {
public:TreeNode* invertTree(TreeNode* root) {if(root == nullptr) return nullptr;swap(root->left, root->right);invertTree(root->left);invertTree(root->right);return root;}
};

101. 对称二叉树

/*** Definition for a binary tree node.* struct TreeNode {*     int val;*     TreeNode *left;*     TreeNode *right;*     TreeNode() : val(0), left(nullptr), right(nullptr) {}*     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}*     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}* };*/
class Solution {
public: bool flag = true;bool isSymmetric(TreeNode* root) {if (!root) return true;return isMirror(root->left, root->right);}bool isMirror(TreeNode* t1, TreeNode* t2) {if (!t1 && !t2) return true; // 都是空，对称if (!t1 || !t2) return false; // 只有一个空，不对称if (t1->val != t2->val) return false; // 值不同，不对称// 左的左 和 右的右，左的右 和 右的左 要分别镜像return isMirror(t1->left, t2->right) && isMirror(t1->right, t2->left);}
};

104. 二叉树的最大深度

/*** Definition for a binary tree node.* struct TreeNode {*     int val;*     TreeNode *left;*     TreeNode *right;*     TreeNode() : val(0), left(nullptr), right(nullptr) {}*     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}*     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}* };*/
class Solution {
public:void countDepth(TreeNode *root, int &result, int &count){if(root == nullptr) return;count++;result = max(result, count);if(root->left) {countDepth(root->left, result, count);}if(root->right){countDepth(root->right, result, count);}count--;}int maxDepth(TreeNode* root) {int result = 0, count = 0;countDepth(root, result, count);return result;}
};

int maxDepth(TreeNode* root) {return root == nullptr ? 0 : max(maxDepth(root->left), maxDepth(root->right)) + 1;}

111. 二叉树的最小深度

/*** Definition for a binary tree node.* struct TreeNode {*     int val;*     TreeNode *left;*     TreeNode *right;*     TreeNode() : val(0), left(nullptr), right(nullptr) {}*     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}*     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}* };*/
class Solution {
public:int minDepth(TreeNode* root) {if(root == nullptr) return 0;int leftHeight = minDepth(root->left);int rightHeight = minDepth(root->right);if(root->left && root->right == nullptr)return leftHeight + 1;if(root->left == nullptr && root->right)return rightHeight + 1;elsereturn min(rightHeight, leftHeight)  + 1;}
};