How should I practice Single-Digit Addition Equation Repairs?

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

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Single-Digit Addition Equation Repairs

ZipRecruiter● MediumNEW GRADOA

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Problem statement

a, b, and c are positive decimal strings containing no zero digits. Change exactly one digit in exactly one input to a different digit from 1 through 9.

Count substitutions after which a + b = c.

Function

countEquationRepairs(a: String, b: String, c: String) → int

Examples

Example 1

a = "7"b = "1"c = "7"return = 2

Changing b to 0 is forbidden; the two valid nonzero repairs satisfy the equation.

Example 2

a = "1"b = "1"c = "2"return = 0

The equation is already true, but exactly one different digit must be changed.

Constraints

1 <= a.length,b.length,c.length <= 15