东哥带你刷二叉树（纲领篇）
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:
int maxDepth(TreeNode* root) {
if (!root) {
return 0;
}
int left = maxDepth(root->left);
int right = maxDepth(root->right);
return left > right ? left + 1 : right + 1;
}
};
/**
* 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 {
private:
int res = 0;
int depth = 0;
public:
int maxDepth(TreeNode* root) {
if (!root) {
return 0;
}
int left = maxDepth(root->left);
int right = maxDepth(root->right);
return left > right ? left + 1 : right + 1;
}
void traverse (TreeNode* root) {
if (root == nullptr) {
return;
}
depth++;
if (root->left == nullptr && root->right == nullptr) {
res = max(res, depth);
}
traverse(root->left);
traverse(root->right);
depth--;
}
};
144. 二叉树的前序遍历
/**
* 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 {
private:
vector<int> preOrder;
public:
vector<int> preorderTraversal(TreeNode* root) {
traverse(root);
return preOrder;
}
void traverse(TreeNode* root) {
if (root == nullptr) return;
preOrder.push_back(root->val);
traverse(root->left);
traverse(root->right);
}
};
543. 二叉树的直径
/**
* 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 {
private:
int res;
public:
int diameterOfBinaryTree(TreeNode* root) {
res = 0;
int traceLength = maxDepth(root->left) + maxDepth(root->right);
return max(traceLength, res);
}
int maxDepth(TreeNode* root) {
if (root == nullptr) return 0;
int left = maxDepth(root->left);
int right = maxDepth(root->right);
int traceLength = left + right;
res = max(traceLength, res);
return max(left, right) + 1;
}
};