public class Solution {
    /**
     * @param a, b, the root of binary trees.
     * @return true if they are identical, or false.
     */
    public boolean isIdentical(TreeNode a, TreeNode b) {
         if(a==null&&b==null){
            return true;
        }
        else if(a==null||b==null){
            return false;
        }
        if(a.val != b.val) return false;
        
        return isIdentical(a.left,b.left)&&isIdentical(a.right,b.right);
    }
}

public class Solution {
    /**
     * @param root: a TreeNode, the root of the binary tree
     * @return: nothing
     */
    public void invertBinaryTree(TreeNode root) {
        if (root == null) return ;
        TreeNode temp = root.left;
        root.left = root.right;
        root.right = temp;
        invertBinaryTree(root.right);
        invertBinaryTree(root.left);
        
    }
}

public class Solution {
    /**
     * @param root: The root of binary tree
     * @return root of new tree
     */
     
    public TreeNode cloneTree(TreeNode root) {
       if(root == null) return null;
       TreeNode res = new TreeNode(root.val);
       res.left = cloneTree(root.left);
       res.right = cloneTree(root.right);
       return res;
    }
}

public class Solution {
    /**
     * @param root: The root of binary tree.
     * @return: An integer.
     */
     
    public int minDepth(TreeNode root) {
         if (root == null) return 0;
        if (root.left == null && root.right == null) return 1;
        if(root.left == null) return minDepth(root.right)+1;
        if(root.right == null) return minDepth(root.left)+1;
        return Math.min(minDepth(root.left),minDepth(root.right))+1;
    }
   
}

public class Solution {
    /**
     * @param root the root of binary tree
     * @return the max ndoe
     */
     TreeNode res = new TreeNode(Integer.MIN_VALUE);
    public TreeNode maxNode(TreeNode root) {
        if(root == null) return null;
        else if(root.val > res.val) res = root;
        maxNode(root.left);
        maxNode(root.right);
        return res;    
    }
}