LeetCode 100. Same Tree

Description

https://leetcode.com/problems/same-tree/

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:

Input: p = [1,2,3], q = [1,2,3]
Output: true

Example 2:

Input: p = [1,2], q = [1,null,2]
Output: false

Example 3:

Input: p = [1,2,1], q = [1,1,2]
Output: false

Constraints:

  • The number of nodes in both trees is in the range [0, 100].
  • -104 <= Node.val <= 104

Explanation

Our goal is to implement isSameTree(TreeNode p, TreeNode q) function.

There are two scenarios for isSameTree(TreeNode p, TreeNode q) to return true:

  1. p and q are both null
  2. when p and q aren’t null, p and q should have same value and p’s left and right subtrees should be same as q’s left and q.right subtrees.

Java Solution

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    public boolean isSameTree(TreeNode p, TreeNode q) {
        if (p == null && q == null) {
            return true;
        }
        
        if (p != null && q != null) {
            if (p.val == q.val && isSameTree(p.left, q.left) && isSameTree(p.right, q.right)) {
                return true;
            }            
        }
        
        return false;
    }
}

Python Solution

# 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: TreeNode, q: TreeNode) -> bool:
        
        return self.helper(p, q)
    
    def helper(self, p, q):
        if not p and not q:
            return True
        
        if not p or not q:
            return False
        
        if p.val != q.val:
            return False
        
        return self.helper(p.left, q.left) and self.helper(p.right, q.right)
  • Time Complexity: O(N)
  • Space Complexity: O(logN)

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