How should I practice Collapse Equal Adjacent Pairs?

Start by reading the full statement, solve the visible examples, then compare the pattern against related Hudson River Trading online assessment problems in FastPrep.

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Collapse Equal Adjacent Pairs

Hudson River Trading● EasyFULLTIMEOA

Problem statement

You are given a string s of uppercase English letters.

While the string has two equal letters next to each other, remove both of them. The letters on each side then become neighbors, which can create a new equal pair. Keep going until no two neighboring letters are equal, and return the final string.

The final string is the same no matter which pair you remove first. It can be the empty string.

Function

collapseEqualPairs(s: String) → String

Examples

Example 1

s = "ABBCDDC"return = "A"

Remove DD to get ABBCC. Then remove CC to get ABB, and remove BB to get A. A single letter has no neighbor, so the answer is "A".

Example 2

s = "AABBAA"return = ""

Remove BB to get AAAA. Remove one AA pair to get AA, then remove that pair too. Nothing is left, so the answer is the empty string.

Example 3

s = "BAAAB"return = "BAB"

Removing one pair from AAA leaves a single A, which gives BAB. The two B letters are not next to each other, so nothing else can be removed and the answer is "BAB".

Example 4

s = "ABCD"return = "ABCD"

No two neighboring letters are equal, so nothing is removed.

Constraints

1 <= s.length <= 10^5
s contains only uppercase English letters 'A' to 'Z'.