How should I practice Count Digit Replacements with No Equal Adjacent Digits?

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

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Count Digit Replacements with No Equal Adjacent Digits

Microsoft● MediumNEW GRADINTERNOA

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Problem statement

You are given a string s containing digits from 0 through 9 and question marks.

Replace every ? with one digit so that no two adjacent digits are equal. Return the number of valid replacements modulo 10^9 + 7.

Function

getNumOfWays(s: String) → int

Examples

Example 1

s = "1?3?"return = 72

The first question mark may be any digit except 1 and 3, giving 8 choices. The last may be any digit except 3, giving 9 choices. Therefore the result is 8 * 9 = 72.

Example 2

s = "??"return = 90

The first position has 10 choices, and the second has 9 choices different from the first.

Constraints

1 <= s.length <= 10^5
s contains only digits from 0 through 9 and ?.