How should I practice Find the Wrong Digit Index in a Sum?

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

Is Find the Wrong Digit Index in a Sum associated with Upstart?

FastPrep tags this as a Upstart online assessment coding practice problem when the problem catalog has that company and stage context.

Problem · Math

Find the Wrong Digit Index in a Sum

Learn this problem

● Easy

UpstartFULLTIMEOA

Problem statement

You are given three non-negative integers: num1, num2, and givenSum.

Compute the correct result of num1 + num2, then compare it with givenSum digit by digit in base 10, starting from the least significant digit (index 0).

The ones place is index 0, the tens place is index 1, and so on. If the correct sum and givenSum have different numbers of digits, treat the missing higher-order digits of the shorter number as 0 when comparing. The comparison continues through the maximum number of digit positions across both numbers.

Return the index of the first mismatching digit. Return -1 if every digit matches (i.e., givenSum equals num1 + num2).

Function

findWrongDigitIndex(num1: long, num2: long, givenSum: long) → int

Complete the function findWrongDigitIndex in the editor below.

findWrongDigitIndex has the following parameters:

long num1: the first addend
long num2: the second addend
long givenSum: the sum to compare against

Returns

int: the index of the first mismatching digit (starting from 0 at the ones place), or -1 if all digits match.

Examples

Example 1

num1 = 13num2 = 7givenSum = 19return = 0

The correct sum is 20. The ones digit differs immediately: 0 versus 9.

Example 2

num1 = 95num2 = 5givenSum = 100return = -1

The provided sum is correct, so there is no mismatching digit.

Constraints

Constraints:

0 <= num1, num2, givenSum <= 10¹⁸
The correct sum num1 + num2 may exceed 10¹⁸; use arbitrary-precision arithmetic when computing the correct sum.
Digits are compared in base 10 from least significant (index 0) to most significant position.
Missing higher-order digits are treated as 0 when the correct sum and givenSum have different numbers of digits.
Return -1 if and only if givenSum == num1 + num2.