leetcode1305 All Elements in Two Binary Search Trees

"""
Given two binary search trees root1 and root2.
Return a list containing all the integers from both trees sorted in ascending order.
Example 1:
Input: root1 = [2,1,4], root2 = [1,0,3]
Output: [0,1,1,2,3,4]
Example 2:
Input: root1 = [0,-10,10], root2 = [5,1,7,0,2]
Output: [-10,0,0,1,2,5,7,10]
Example 3:
Input: root1 = [], root2 = [5,1,7,0,2]
Output: [0,1,2,5,7]
Example 4:
Input: root1 = [0,-10,10], root2 = []
Output: [-10,0,10]
Example 5:
Input: root1 = [1,null,8], root2 = [8,1]
Output: [1,1,8,8]
"""
class TreeNode:
    def __init__(self, x):
        self.val = x
        self.left = None
        self.right = None

"""
此题提供三种思路，与leetcode98类似，https://www.cnblogs.com/yawenw/p/12376942.html
第一种是层次遍历，
然后对存入的值sorted排序
传送门:https://blog.csdn.net/qq_17550379/article/details/103838538
"""
class Solution1:
    def getAllElements(self, root1, root2):
        q, res = [root1, root2], []
        while q:
            cur = q.pop(0)
            if cur:
                res.append(cur.val)
                if cur.left != None:
                    q.append(cur.left)
                if cur.right != None:
                    q.append(cur.right)
        return sorted(res)

"""
第二种是利用二叉搜索树的条件，
对两个树分别中序遍历。这样两个list分别有序
再进行归并排序
"""
class Solution2:
    def getAllElements(self, root1, root2):
        q1, q2 = [], []
        res = []
        # 中序遍历
        def inorder(root, q):
            if root:
                inorder(root.left, q)
                q.append(root.val)
                inorder(root.right, q)
        inorder(root1, q1)
        inorder(root2, q2)
        # 归并排序的方法
        while q1 or q2:
            if not q1:
                res += q2
                break
            if not q2:
                res += q1
                break
            else:
                res.append(q1.pop(0) if q1[0] < q2[0] else q2.pop(0))
        return res

"""
第三种是：
先中序遍历(代替层次遍历)
再sorted(代替归并排序)
"""
class Solution3:
    def getAllElements(self, root1, root2):
        res = []
        def inOrder(root):
            if root:    #!!!bug 没有写次if语句
                inOrder(root.left)
                res.append(root.val)
                inOrder(root.right)
        inOrder(root1)
        inOrder(root2)
        return sorted(res)