sooditk / github-externship-assignment

Github Externship Assignment

Problem statement

You are given a String equation containing an equation of the form A * B + C = D, where A, B, C and D are positive integers that don't have leading zeros.
One digit in the equation is missing.
Determine and return the correct digit.
If the missing digit cannot be determined (i.e., there is no solution or there is more than one solution), return -1 instead.

Definition

• Class: FixEquation
• Method : findMissingDigit
• Parameters : String
• Returns : Integer
• Method signature : function findMissingDigit(equation)

Note: A digit is correct if and only if it produces a valid equation in which A, B, C and D are positive integers with no leading zeros.

Constraints

• Equation will have the form A * B + C = D.
• Each of A, B, C, D will be a nonempty string of 1 to 4 characters, i.e., 1 <= length of A, B, C, D <= 4.
• Each character in each of A, B, C, D will be either a digit ('0'-'9') or a question mark ('?').
• There will be exactly one question mark in equation.
• The numbers represented by A, B, C, D will not have leading zeros.

Test Cases

1️⃣

Equation: 42 * 47 + 2 = 1?76

Returns: 9

We know that 42 * 47 + 2 = 1974, so the missing digit is 9.

2️⃣

Equation: 4? * 47 + 2 = 1976

Returns: 2

The same equation, another missing digit.

3️⃣

Equation: 42 * ?7 + 2 = 1976

Returns: 4

And again the same equation.

4️⃣

Equation: 42 * ?47 + 2 = 1976

Returns: -1

This test case has no valid solution. The numbers cannot have leading zeros, so we cannot fill in a zero in front of 47.

5️⃣

Equation: 2 * 12? + 2 = 247

Returns: -1

Two times something + 2 will never be 247, so this test case has no solution either.