144. 二叉树的前序遍历
cpp
复制代码
/**
* 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:
vector<int>ret;
void pre(TreeNode* root){
if(root != nullptr){
ret.push_back(root->val);
pre(root->left);
pre(root->right);
}
}
vector<int> preorderTraversal(TreeNode* root) {
pre(root);
return ret;
}
};
102. 二叉树的层序遍历
cpp
复制代码
/**
* 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:
vector<vector<int>> levelOrder(TreeNode* root) {
vector<vector<int>>ret;
if(!root) return ret;
queue<TreeNode*>q;
q.push(root);
while(!q.empty()){
vector<int>level;
int size = q.size();
for(int i = 0; i < size; i++){
TreeNode* temp = q.front();
q.pop();
level.push_back(temp->val);
if(temp->left) q.push(temp->left);
if(temp->right) q.push(temp->right);
}
ret.push_back(level);
}
return ret;
}
};
199. 二叉树的右视图
cpp
复制代码
/**
* 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:
vector<int> rightSideView(TreeNode* root) {
vector<int>ret;
if(!root) return ret;
queue<TreeNode*>q;
q.push(root);
while(!q.empty()){
int size = q.size();
for(int i = 0; i < size; i++){
TreeNode* temp = q.front();
q.pop();
if(i == size - 1){
ret.push_back(temp->val);
}
if(temp->left) q.push(temp->left);
if(temp->right) q.push(temp->right);
}
}
return ret;
}
};
404. 左叶子之和
cpp
复制代码
/**
* 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 traverse(TreeNode* root, bool is_left){
if(!root) return 0; // 节点为空
if(!root->left && !root->right && is_left) return root->val; // 叶子节点且为左子树
return traverse(root->left, true) + traverse(root->right, false);
}
int sumOfLeftLeaves(TreeNode* root) {
// 三种情况：1. 节点为空；2. 叶子节点且为左子树 ; 3. else
return traverse(root, false);
}
};
104. 二叉树的最大深度
cpp
复制代码
/**
* 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) {
// 1. 有左右儿子，2. 空, 3. else
if(!root) return 0;
int max_v = 1;
if(root->left) max_v = maxDepth(root->left) + 1;
if(root->right) max_v = max(max_v, maxDepth(root->right) + 1);
return max_v;
}
};