leetcode-面试题32 ①②③

题一：

 

 提交：层序遍历bfs O(N) O(N)

class Solution:
    def levelOrder(self, root: TreeNode) -> List[int]:
        if not root : return []
        queue = [root]
        res = []
        while queue:
            #for i in range(len(queue)):
                cur = queue.pop(0)
                res.append(cur.val)
                if cur.left:
                    queue.append(cur.left)
                if cur.right:
                    queue.append(cur.right)
        return res

题二：

 

 提交：

class Solution:
    def levelOrder(self, root: TreeNode) -> List[List[int]]:
        if not root:return []
        res = []
        queue = [root]
        while queue:
            digit = []
            tmp = []
            for i in queue:
                digit.append(i.val)
                if i.left:tmp.append(i.left)
                if i.right:tmp.append(i.right)
            res.append(digit)
            queue = tmp[:]
        return res

题三：

 

 

class Solution:
    def levelOrder(self, root: TreeNode) -> List[List[int]]:
        if not root:return []
        res = []
        queue = [root]
        m = 0
        while queue:
            tmp = []
            for i in range(len(queue)):
                node = queue.pop(0)
                tmp.append(node.val)
                if node.left: queue.append(node.left)
                if node.right: queue.append(node.right)
            if m % 2 == 0:
                res.append(tmp)
            else:
                res.append(tmp[::-1])
            m += 1
        return res