What is the time complexity of Check If Digits Are Equal in String After Operations I?

The optimal solution for Check If Digits Are Equal in String After Operations I runs in O(n) time and uses O(1) space. We only traverse the string once to sum the digits, leading to O(n) complexity.

What is the brute force solution for Check If Digits Are Equal in String After Operations I?

The brute force approach for Check If Digits Are Equal in String After Operations I is Brute Force, with O(n²) time complexity and O(1) space complexity. We repeatedly simulate the operations on the string until it reduces to two digits. This method directly follows the problem statement but can be inefficient. The optimal Optimal Solution approach improves this to O(n).

What are the interview tips for Check If Digits Are Equal in String After Operations I?

Explain your thought process clearly. Consider edge cases like single-digit strings. Practice similar problems to build intuition.

What are common mistakes when solving Check If Digits Are Equal in String After Operations I?

Not considering the modulo operation correctly. Overlooking the need to reduce to two digits.

#3461

Check If Digits Are Equal in String After Operations I

Easy

MathStringSimulationCombinatoricsNumber TheorySimulationMathematical Operations

LeetCode ↗

Approaches

Brute ForceOptimal

Complexity Comparison

	Brute Force	Optimal Solution★
Time	O(n²)	O(n)
Space	O(1)	O(1)

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Intuition

Time O(n)Space O(1)

Instead of simulating the entire process, we can observe that the final digits depend only on the parity of the sums of the original digits.

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Algorithm

3 steps

1Step 1: Calculate the sum of the digits in the string.
2Step 2: Check if the last two digits of this sum (modulo 10) are equal.
3Step 3: Return true if they are equal, otherwise return false.

solution.py3 lines

1def checkEqualDigits(s):
2    total = sum(int(d) for d in s)
3    return (total % 10) == ((total // 10) % 10)

ℹ

Complexity note: We only traverse the string once to sum the digits, leading to O(n) complexity.

1The final digits depend on the sum of the original digits.
2Modulo 10 operations simplify the problem.

Solutions and explanations are original Tejav content. Problem titles © LeetCode — use the LeetCode button above for the full problem statement.