1. 103. Binary Tree Zigzag Level Order Traversal

    # 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 zigzagLevelOrder(self, root):
        """
        :type root: TreeNode
        :rtype: List[List[int]]
        """
        if root == None:
            return []
        queue = [root]
        result = []
        count = 0
        while queue:
            newq = []
            newr = []
            for ...
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  2. 102. Binary Tree Level Order Traversal

    import Queue
# 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 levelOrder(self, root):
        """
        :type root: TreeNode
        :rtype: List[List[int]]
        """
        if root == None:
            return []
        queue = Queue.Queue()
        queue.put(root)  # record each ...
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  3. 101. Symmetric Tree

    # 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 isSymmetric(self, root):
        """
        :type root: TreeNode
        :rtype: bool
        """
        if root == None:
            return True
        return self.help(root.left, root.right)

    def help(self, p ...
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  4. 100. Same Tree

    # 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 isSameTree(self, p, q):
        """
        :type p: TreeNode
        :type q: TreeNode
        :rtype: bool
        """
        if p == None and q == None:
            return True
        if p and q ...
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  5. 98. Validate Binary Search Tree

    # 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 isValidBST(self, root):
        """
        :type root: TreeNode
        :rtype: bool
        """
        return self.dfs(root, min=float('-inf'), max=float('inf'))

    def dfs(self, root, min, max ...
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  6. 96. Unique Binary Search Trees

    class Solution(object):
    def numTrees(self, n):
        """
        :type n: int
        :rtype: int
        """
        nums = [0] * (n + 1)
        nums[0] = 1
        nums[1] = 1
        if n == 0 or n == 1:
            return 1
        for i in range(2, n + 1):
            result = 0
            for j in range(0, i):
                result += nums[j] * nums[i ...
    read more

  7. 95. Unique Binary Search Trees II

    # 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 generateTrees(self, n):
        """
        :type n: int
        :rtype: List[TreeNode]
        """
        if n == 0:
            return []
        return self.dfs(1, n)

    def dfs(self, start, end):
        if ...
    read more

  8. 94. Binary Tree Inorder Traversal

    # 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 inorderTraversal(self, root):
        """
        :type root: TreeNode
        :rtype: List[int]
        """
        if root is None:
            return []
        return self.inorderTraversal(root.left) + [root.val]\
            + self.inorderTraversal(root ...
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  9. 93. Restore IP Addresses

    class Solution(object):
    def restoreIpAddresses(self, s):
        """
        :type s: str
        :rtype: List[str]
        """
        ans = []
        self.helper(ans, s, 4, [])
        return ['.'.join(x) for x in ans]

    def helper(self, ans, s, k, temp):
        if len(s) > k * 3:
            return ''
        elif k == 0:
            ans.append(temp)
        else:
            for i in range ...
    read more

  10. 92. Reverse Linked List II

    # Definition for singly-linked list.
# class ListNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.next = None

class Solution(object):
    def reverseBetween(self, head, m, n):
        """
        :type head: ListNode
        :type m: int
        :type n: int
        :rtype: ListNode
        """
        if m == n:
            return head

        cons = ListNode(0)
        cons.next = head
        cur = cons ...
    read more

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