Good morning! Here's our prompt for today.

You're given an array of strings containing alphabetical characters and certain $ characters. A $ represents a DELETE action whereby the character before it is deleted.

Each of these strings will be run through a method to operate on the $ DELETE action. We want to find out if the final string is the same for all of them. Let's take an example:

1input = ["f$st", "st"]
2is_dollar_delete_equal(input)
3# True
4# True because both become 'st'

Can you find a solution in O(n) time and constant space?

Constraints

• The input arrays can be of any size
• Every string has at least a single character
• The string will consist of dollar signs and lowercase alphabets
• Expected overall time complexity : O(n)
• Expected space complexity : O(n) for good solution, O(1) for asymptotically optimal solution

Try to solve this here or in Interactive Mode.

How do I practice this challenge?

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def is_dollar_delete_equal(arr):

    # fill in

    return arr

​

​

import unittest

​

​

class Test(unittest.TestCase):

    def test_1(self):

        assert is_dollar_delete_equal(["f$ec", "ec"]) == True

        print("PASSED: `['f$ec', 'ec']` should return `true`")

​

    def test_2(self):

        assert is_dollar_delete_equal(["a90$n$c$se", "a90n$cse"]) == False

        print("PASSED: `['a90$n$c$se', 'a90n$cse']` should return `false`")

​

    def test_3(self):

        assert is_dollar_delete_equal(["ab$$", "c$d$"]) == True

        print("PASSED: `['ab$$', 'c$d$']` should return `true`")

​

    def test_4(self):

        assert is_dollar_delete_equal(["b$$p", "$b$p"]) == True

        print("PASSED: `['b$$p', '$b$p']` should return `true`")

​

​

if __name__ == "__main__":

    unittest.main(verbosity=2)

    print("Nice job, 4/4 tests passed!")

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