100. Same Tree
Given two binary trees, write a function to check if they are the same or not.
Two binary trees are considered the same if they are structurally identical and the nodes have the same value.
Example 1:
Input: 1 1
/ /
2 3 2 3
[1,2,3], [1,2,3]
Output: true
Example 2:
Input: 1 1
/
2 2
[1,2], [1,null,2]
Output: false
Example 3:
Input: 1 1
/ /
2 1 1 2
[1,2,1], [1,1,2]
Output: false
# 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
"""
return p.val==q.val and self.isSameTree(p.left, q.left) and self.isSameTree(p.right, q.right) if p and q else p is q
# one liner
104. Maximum Depth of Binary Tree
Given a binary tree, find its maximum depth.
The maximum depth is the number of nodes along the longest path from the root node down to the farthest leaf node.
# 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 maxDepth(self, root):
"""
:type root: TreeNode
:rtype: int
"""
if(root is None):
return 0
return max(self.maxDepth(root.left),self.maxDepth(root.right))+1
107. Binary Tree Level Order Traversal II
Given a binary tree, return the bottom-up level order traversal of its nodes' values. (ie, from left to right, level by level from leaf to root).
For example:
Given binary tree [3,9,20,null,null,15,7],
3
/
9 20
/
15 7
return its bottom-up level order traversal as:
[ [15,7], [9,20], [3] ]
# 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 levelOrderBottom(self, root):
"""
:type root: TreeNode
:rtype: List[List[int]]
"""
res, queue = [], [root]
while queue:
res.append([node.val for node in queue if node])
queue = [child for node in queue if node for child in (node.left, node.right)]
return res[-2::-1]
# elements in each layer should be contained in a list
# res[-2::-1] will reverse the list res[0:-2]
108. Convert Sorted Array to Binary Search Tree
Given an array where elements are sorted in ascending order, convert it to a height balanced BST.
For this problem, a height-balanced binary tree is defined as a binary tree in which the depth of the two subtrees of every node never differ by more than 1.
Example:
Given the sorted array: [-10,-3,0,5,9],
One possible answer is: [0,-3,9,-10,null,5], which represents the following height balanced BST:
0
/
-3 9
/ /
-10 5
# 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 sortedArrayToBST(self, nums):
"""
:type nums: List[int]
:rtype: TreeNode
"""
if not nums:
return None
mid = len(nums) // 2
root = TreeNode(nums[mid])
root.left = self.sortedArrayToBST(nums[:mid])
root.right = self.sortedArrayToBST(nums[mid+1:])
return root
# !!!!! when a == [] , a is not None !!!!!!!!!!
111. Minimum Depth of Binary Tree
Given a binary tree, find its minimum depth.
The minimum depth is the number of nodes along the shortest path from the root node down to the nearest leaf node.
# 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 minDepth(self, root):
"""
:type root: TreeNode
:rtype: int
"""
if(root is None): return 0
if(root.left is None and root.right is None): return 1
if(root.left is None or root.right is None): return (max(self.minDepth(root.left),self.minDepth(root.right))+1)
else: return (min(self.minDepth(root.left),self.minDepth(root.right))+1)
# a bit more difficult than the maxDepth one
110. Balanced Binary Tree
Given a binary tree, determine if it is height-balanced.
For this problem, a height-balanced binary tree is defined as a binary tree in which the depth of the two subtrees of every node never differ by more than 1.
# 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 isBalanced(self, root):
"""
:type root: TreeNode
:rtype: bool
"""
def depth(root):
if root is None: return 0
dep_l = depth(root.left)
dep_r = depth(root.right)
if dep_l == -1 or dep_r == -1 or abs(dep_l - dep_r)>1:
return -1
return max(dep_l, dep_r)+1
return depth(root) != -1
# use a special number as a sign of unqualified tree
112. Path Sum
Given a binary tree and a sum, determine if the tree has a root-to-leaf path such that adding up all the values along the path equals the given sum.
For example:
Given the below binary tree and sum = 22,
5
/
4 8
/ /
11 13 4
/
7 2 1
return true, as there exist a root-to-leaf path 5->4->11->2 which sum is 22.
# 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 hasPathSum(self, root, sum):
"""
:type root: TreeNode
:type sum: int
:rtype: bool
"""
if root is None: return False
if root.left is None and root.right is None and sum == root.val: return True
return self.hasPathSum(root.left,sum-root.val) or self.hasPathSum(root.right,sum-root.val)