File: sum-of-digits-in-the-minimum-number/solution.py

Date: 2026-06-06

Time: 19:21

Purpose

This file solves LeetCode 1085 — Sum of Digits in the Minimum Number. It owns a single responsibility: given an array of positive integers, find the minimum element, sum its digits, and return 1 if that sum is even, 0 if odd.

Key Components

Solution.sumofdigits(self, nums: List[int]) -> int

The only method. Its contract:

• Input: nums — a non-empty list of positive integers.
• Output: 1 if the digit sum of min(nums) is even, 0 if odd.
• Side effects: None.

Patterns

Digit extraction via modular arithmetic. Rather than converting to a string and summing character values (sum(int(d) for d in str(min_val))), the solution uses the classic % 10 / // 10 loop. This avoids string allocation and is a common idiom in LeetCode number-manipulation problems.

Destructive iteration on a copy. min_val is consumed by the while loop — its value is zero when the loop exits. This is fine because the original list isn't mutated; min() returned a value, not a reference to the list element.

Dependencies

• Imports: typing.List — used only for the type annotation on nums.
• Imported by: sum-of-digits-in-the-minimum-number/test_solution.py (directly). The massive "Imported By" list in the prompt is an artifact of the repo's shared test infrastructure — those other test files don't actually import this solution.

Flow

1. min(nums) scans the list in O(n) to find the smallest element.

2. The while loop extracts digits from right to left, accumulating their sum. It terminates when min_val reaches 0 (integer division of a single digit by 10).

3. The ternary at the return checks parity of the digit sum.

Invariants

• nums must be non-empty — min() raises ValueError on an empty sequence.
• All elements must be positive integers (per the problem constraints). The digit-extraction loop works correctly for any non-negative integer, but min_val = 0 would skip the loop entirely and return 1 (digit sum 0 is even), which is technically correct but outside the stated constraint.

Error Handling

None. The function trusts its caller to provide valid input per LeetCode conventions. An empty list would propagate ValueError from min().

Topics to Explore

• [file] sum-of-digits-in-the-minimum-number/test_solution.py — See the test cases and edge cases exercised for this solution
• [file] sum-of-digits-in-the-minimum-number/review.md — Code review notes that may flag alternative approaches or pitfalls
• [function] add-digits/solution.py:Solution.addDigits — A related digit-sum problem that uses the digital root formula instead of a loop
• [function] subtract-the-product-and-sum-of-digits-of-an-integer/solution.py:Solution.subtractProductAndSum — Compare digit-extraction patterns across similar problems
• [general] digit-extraction-idiom — Whether the repo consistently uses mod-arithmetic vs string conversion for digit problems

Beliefs

• digit-sum-min-returns-binary — sumofdigits returns exactly 0 or 1, never any other value
• digit-extraction-uses-mod-arithmetic — Digits are extracted via % 10 / // 10 rather than string conversion
• min-scan-is-linear — The minimum is found with a single min() call (O(n)), not by sorting
• no-input-validation — The function does not guard against empty lists or non-positive values; it relies on LeetCode's problem constraints