1. 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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  2. About

    Hello, I'm Haven Shi, a software developer at NJ. I’m passionate about using technology to work more effectively. Right now I’m working on big data platform and UI projects, with various technologies including Java, Python, Scala, Hadoop, Spark Streaming, SQL, and Spring Framework. I have years of ...

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  3. 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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  4. 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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  5. 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 ...
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  6. 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 ...
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  7. 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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  8. 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 ...
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  9. 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 ...
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  10. Personified Bank's Department Characters

    These pictures are drawn when I worked in Bank of China.

    Personified characters has a growing popularity in Japan. It means draw a series of things, like food, courses, countries or even programming language as certain kinds of cartoon characters. It could be also used to departments.

    When I worked ...

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