春节刷题day5：LeetCode
122. 买卖股票的最佳时机 II
104. 二叉树的最大深度
226. 翻转二叉树
617. 合并二叉树
543. 二叉树的直径
122. 买卖股票的最佳时机 II
class Solution {
public:
int maxProfit(vector<int>& prices) {
int ans = 0;
for(int i = 1; i < prices.size(); i++){
if(prices[i] > prices[i - 1]) ans += prices[i] - prices[i - 1];
}
return ans;
}
};
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 == NULL) return 0;
return max(maxDepth(root -> left), maxDepth(root -> right)) + 1;
}
};
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 == NULL) return NULL;
swap(root -> right, root -> left);
invertTree(root -> right);
invertTree(root -> left);
return root;
}
};
617. 合并二叉树
/**
* 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* mergeTrees(TreeNode* root1, TreeNode* root2) {
if(root1 == NULL) return root2;
if(root2 == NULL) return root1;
TreeNode* ans = new TreeNode(0);
ans -> val = root1 -> val + root2 -> val;
ans -> left = mergeTrees(root1 -> left, root2 -> left);
ans -> right = mergeTrees(root1 -> right, root2 -> right);
return ans;
}
};
543. 二叉树的直径
/**
* Definition for a binary tree node.
* struct TreeNode {
* int val;
* TreeNode *left;
* TreeNode *right;
* TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class Solution {
public:
int ans = 0;
int depth(TreeNode* root){
if(root == NULL) return 0;
int l = depth(root -> left);
int r = depth(root -> right);
ans = max(ans, l + r);
return max(l, r) + 1;
}
int diameterOfBinaryTree(TreeNode* root) {
depth(root);
return ans;
}
};
未完待续······。