What does "return x and y" mean?

Question

I'm solving a question to check for a Balanced Binary Tree. It states that:

Given a binary tree, find if it is height balanced or not. A tree is height balanced if difference between heights of left and right subtrees is not more than one for all nodes of tree.

Example 1:

Input:
      1
    /
   2
    \
     3 
Output: 0
Explanation: The max difference in height
of left subtree and right subtree is 2,
which is greater than 1. Hence unbalanced
Example 2:

Input:
       10
     /   \
    20   30 
  /   \
 40   60
Output: 1
Explanation: The max difference in height
of left subtree and right subtree is 1.
Hence balanced.

Your Task: You don't need to take input. Just complete the function isBalanced() that takes root node as parameter and returns true, if the tree is balanced else returns false.

This is the following solution for the problem:

class Height: 
    def __init__(self): 
        self.height = 0

# helper function to check if binary 
# tree is height balanced 
def isBalancedUtil(root, height): 
      
    # lh and rh to store height of  
    # left and right subtree 
    lh = Height() 
    rh = Height() 
  
    # Base condition when tree is  
    # empty return true 
    if root is None: 
        return True
  
    # l and r are used to check if left 
    # and right subtree are balanced 
    l = isBalancedUtil(root.left, lh) 
    r = isBalancedUtil(root.right, rh) 
  
    # height of tree is maximum of  
    # left subtree height and 
    # right subtree height plus 1 
    height.height = max(lh.height, rh.height) + 1
  
    if abs(lh.height - rh.height) <= 1: 
        return l and r 
  
    # if we reach here then the tree  
    # is not balanced 
    return False
    
def isBalanced(root):
    # to store the height of tree during traversal 
    height = Height() 
    return isBalancedUtil(root,height)

Can anyone tell me what does the return l and r do? What does using and with return do?

`and` does the same with `return` as it does anywhere else. There is nothing special about it used with `return` here. — mkrieger1, Oct 29 '20 at 10:35
Does this answer your question? [How do "and" and "or" act with non-boolean values?](https://stackoverflow.com/questions/47007680/how-do-and-and-or-act-with-non-boolean-values) — mkrieger1, Oct 29 '20 at 10:36
Altough they are not even non-boolean values so this is even less special. What is unclear to you exactly? — mkrieger1, Oct 29 '20 at 10:37

score 0 · Answer 1 · answered Oct 29 '20 at 10:36

0

It uses the logical function r AND l to define the output.

TRUE AND TRUE -> TRUE
TRUE AND FALSE -> FALSE
FALSE AND TRUE -> FALSE
FALSE AND FALSE -> FALSE

answered Oct 29 '20 at 10:36

pygri

647
6
17

score 0 · Answer 2 · answered Oct 29 '20 at 10:38

0

return l and r means return (l and r). It will return the value of the evaluation of (l and r), so true if l and r are true and false if not.

answered Oct 29 '20 at 10:38

GabrielC

322
1
6

But what if ```l``` is 1 and ```r``` is None. Will the output be ```false```then? – Arnav Luhadiya Oct 29 '20 at 10:44
1

If `l` is 1 and `r` is None then `l and r` is equal to None. But in the question, `l` and `r` are booleans, so `l and r` is either True or False. – khelwood Oct 29 '20 at 10:59

What does "return x and y" mean?

2 Answers2