Write a function bool isBalanced$($const std::string& expr$)$ that checks whether a

given expression containing parentheses $(),$ curly braces $\{\},$ and square brackets $[]$ is balanced.

An expression is considered balanced if every opening bracket has a corresponding closing

bracket, and the pairs of brackets are properly nested.

What is the time complexity of the isBalanced function? Explain your answer.

For example:

$$ isBalanced$("()\{\}[]")$ should return true

$$ isBalanced$("([\{\}])")$ should return true

$$ isBalanced$("(]")$ should return false

$$ isBalanced$("([)]")$ should return false