cixuuz

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {

cixuuz

/**
 * Definition for binary tree
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */

cixuuz

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {

cixuuz

public class Solution {
    public int maxDepth(TreeNode root) {
        if (root == null) {
            return 0;
        } 
        
        return Math.max(maxDepth(root.left), maxDepth(root.right)) + 1;
    }
}

cixuuz

public class Solution {
    public int numTrees(int n) {
        int[] dp = new int[n+1];
        
        dp[0] = dp[1] = 1;
            
        for (int i=2; i <= n; i++) {
            for (int j=1; j <= i; j++) {
                dp[i] += dp[j-1] * dp[i-j];
            }

cixuuz

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {

cixuuz

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {

cixuuz

# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution(object):
    def invertTree(self, root):
        """

cixuuz

# Definition for binary tree with next pointer.
# class TreeLinkNode:
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None
#         self.next = None

from collections import deque

cixuuz

class Solution:
    cor = set()
    def findTarget(self, root, k):
        """
        :type root: TreeNode
        :type k: int
        :rtype: bool
        """
        if root is None:
            return False