Problem Statement
Given the roots of two binary trees p and q, 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:
2 2
1 3 1 3
Input: p = [1,2,3], q = [1,2,3]
Output: true
Example 2:
1 1
2 2
Input: p = [1,2], q = [1,null,2]
Output: false
Example 3:
2 1
1 1 1 2
Input: p = [1,2,1], q = [1,1,2]
Output: false
Recursive Implementation
# Definition for a binary tree node.
# class TreeNode:
# def __init__(self, val=0, left=None, right=None):
# self.val = val
# self.left = left
# self.right = right
class Solution:
def isSameTree(self, p: Optional[TreeNode], q: Optional[TreeNode]) -> bool:
"""
* While the values of p and q are equal,
drill down recursively
* If p and q are null, we have a leaf, return True
* Return False for all other cases
* p.val != q.val
* structure differs
"""
# T: O(N) ~ visit each node once
# S: O(N) ~ recursive call stack
if p and q and p.val == q.val:
return self.isSameTree(p.left, q.left) and \
self.isSameTree(p.right, q.right)
elif not p and not q:
return True
else:
return False
Iterative Implementation
# Definition for a binary tree node.
# class TreeNode:
# def __init__(self, val=0, left=None, right=None):
# self.val = val
# self.left = left
# self.right = right
from collections import deque
class Solution:
def isSameTree(self, p: Optional[TreeNode], q: Optional[TreeNode]) -> bool:
"""
* Same as above
"""
queue = deque([(p, q)])
while queue:
p, q = queue.popleft()
if p and q and p.val == q.val:
# Traverse tree while values and
# strcture are equal
queue.append((p.left, q.left))
queue.append((p.right, q.right))
elif not p and not q:
# We have found a leaf.
# No new information here.
pass
else:
# Either the values of p and q
# turned out to be different or
# the structure differed
return False
return True