Check Array Arithmetic Expressions
Reported by candidates from Capital One's online assessment. Pattern, common pitfall, and the honest play if you blank under the timer.
The input size on this Capital One question, reported in September 2026, is the first thing to read, and it's also the reason there's nothing hard here. Arrays go up to 10^5 elements, so you can't do anything quadratic, but you don't need to. It's a single pass over four parallel arrays, checking each index on its own. If your invite says Capital One and you're staring at Check Array Arithmetic Expressions, relax. It's a warm-up with a couple of small traps. StealthCoder sits on your screen as a safety net in case you blank mid-assessment, but this one is mostly about not overthinking.
The problem
You are given three equal-length integer arrays a, b, and c, together with an equal-length character array signs. Each element of signs is either '+' or '-'. Return a boolean array result of the same length, where result[i] is true exactly when applying signs[i] to a[i] and b[i] produces c[i]. If signs[i] == '+', check whether a[i] + b[i] == c[i]. If signs[i] == '-', check whether a[i] - b[i] == c[i]. Function checkArithmeticExpressions(a: int[], signs: char[], b: int[], c: int[]) → boolean[] Examples Example 1 a = [3,2,-1,4] signs = ["+","-","-","+"] b = [2,7,-5,2] c = [5,5,4,2] return = [true,false,true,false] The four checks are 3 + 2 = 5, 2 - 7 != 5, -1 - (-5) = 4, and 4 + 2 != 2. Constraints 1 <= a.length == b.length == c.length == signs.length <= 10^5 -10^9 <= a[i], b[i], c[i] <= 10^9 Every value in signs is either '+' or '-'. Every evaluated addition or subtraction fits a signed 32-bit integer.
Reported by candidates. Source: FastPrep
Pattern and pitfall
The pattern is plain array iteration. For each index i, look at signs[i], compute a[i] + b[i] or a[i] - b[i], compare to c[i], and write true or false into the result. That's O(n) time and O(n) space for the output. Brute force isn't even a temptation, because each index is independent. No sorting, no hash map, no prefix tricks. The pitfalls are small. First, the sign is a character, so compare against '+' and not a string in languages that care. Second, watch the types. The constraints say every evaluated result fits in signed 32-bit, but a[i] - b[i] on values near 10^9 can still be risky in some setups, so use a 64-bit integer if you're unsure. Third, keep the output length equal to the input length. If you freeze on the function signature or the parameter order (a, signs, b, c), StealthCoder can hand you the loop as a hedge during the live OA.
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Check Array Arithmetic Expressions FAQ
How hard is Check Array Arithmetic Expressions really?+
Easy. It's one loop over parallel arrays with a branch on the sign. If you can write a for loop and an if statement, you can solve it. The only real risk is a careless mistake, like mixing up the parameter order or mishandling negative numbers.
What's the trick to this Capital One question?+
There isn't one. Each index is independent, so you evaluate a[i] plus or minus b[i] and compare to c[i]. The work is reading carefully: the parameters come in the order a, signs, b, c, and the result is a boolean array matching the input length.
Do I need to worry about integer overflow?+
The constraints guarantee every evaluated addition or subtraction fits a signed 32-bit integer, so you're mostly safe. If you want zero doubt, cast to a 64-bit type before computing. It costs nothing and removes the whole question in languages with fixed-width ints.
What time and space complexity should I state?+
O(n) time because you visit each index once, and O(n) space for the result array. Auxiliary space beyond the output is O(1). With n up to 10^5, that's comfortably fast, and anything slower than linear would be unnecessary.
How do I prepare for this in 48 hours?+
Don't cram this exact problem. Practice simple array loops with a conditional, and edge cases like negatives and the largest values. Then spend your time on the harder problems an OA tends to pair with an easy one, since this one is the quick win.