LeetCode 3697: Compute Decimal Representation ·

Table of Contents

Meta Data
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Difficulty: easy First Attempt: 2025-09-28

Submissions: Accepted (first try)

Approach
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A component is “one digit 1–9 × a power of 10”, so each non-zero digit maps to exactly one component, e.g. 537 = 500 + 30 + 7. Zero digits need none. That is the minimum, since each component covers only one digit.

Take digits from the low end with % 10 while tracking the place value place, then reverse into descending order.

My Solution
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class Solution:
    def decimalRepresentation(self, n: int) -> List[int]:
        res = []
        place = 1
        while n:
            d = n % 10
            if d:
                res.append(d * place)
            n //= 10
            place *= 10
        return res[::-1]                   # descending

I originally built each component as a string f"{r}{'0' * zeros}"; multiplying by place is more direct.

Complexity
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Time O(d) for d digits, space O(d).

Mistakes to Avoid
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Skip zero digits.
Digits come out from the low end, so reverse at the end.

Interview Explanation
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Each non-zero digit times its place value is one component, and a component can only represent one digit, so this is minimal. I peel digits with % 10, skip zeros, and reverse into descending order. Time O(d).