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Problem · String

Largest Number With Even Digit Frequencies

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● Easy

DRWNEW GRADOA

Problem statement

You are given a string digits containing only the digits 1 and 2.

Delete zero or more characters without changing the relative order of the characters that remain. In the resulting string, both 1 and 2 must occur an even number of times; zero occurrences of a digit is allowed.

Return the numerically largest valid remaining string.

Function

solution(digits: String) → String

Examples

Example 1

digits = "121212"return = "2121"

Each digit occurs three times, so one 1 and one 2 must be removed. Removing the first 1 and the last 2 produces 2121, the largest valid result.

Example 2

digits = "2121122"return = "221122"

The string has three 1s and four 2s. Removing the first 1 makes both frequencies even and yields 221122.

Example 3

digits = "1111"return = "1111"

The four 1s already have even frequency, so keeping every character gives the largest result.

Constraints

3 <= digits.length <= 200000.
digits contains only 1 and 2.