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. 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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  3. 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 ...
    read more

  4. 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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  5. 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

  6. 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 ...
    read more

  7. 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

  8. 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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  9. 91. Decode Ways

    class Solution(object):
    def numDecodings(self, s):
        """
        :type s: str
        :rtype: int
        """
        code = ['10', '11', '12', '13', '14', '15', '16', '17', '18', '19', '20', '21', '22', '23', '24', '25', '26']
        if s == "" or s[0] == '0':
            return 0
        dp = [0 for x in range(len(s)+1)]
        dp[0] = 1 ...
    read more

  10. 90. Subsets II

    class Solution(object):
    def subsetsWithDup(self, nums):
        """
        :type nums: List[int]
        :rtype: List[List[int]]
        """
        nums.sort()
        total = [[]]
        for i in range(1, len(nums) + 1):
            total += self.subsets_each(nums, i)
        return total

    def subsets_each(self, array, target):
        self.result = []
        for i in range(len(array)):
            self.helper([array[i ...
    read more

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