Is Smallest Index With Digit Sum Equal to Index easy or hard?

Smallest Index With Digit Sum Equal to Index is categorized as an Easy problem. It mainly tests basic array traversal and digit manipulation. The challenge lies in implementing the digit sum correctly and remembering to return the smallest valid index.

Smallest Index With Digit Sum Equal to Index Python/Java solution

Implement a loop over the array indices. For each index i, compute the digit sum of nums[i] using modulo and division operations, then compare it with i. Return the first index where they match; otherwise return -1 after the loop. The same logic translates directly to Python, Java, C++, Go, and TypeScript.

How to solve Smallest Index With Digit Sum Equal to Index in O(n)?

Traverse the array once and compare each index with the digit sum of the corresponding value. By computing the digit sum efficiently and stopping at the first valid match, the algorithm performs a single pass through the array. The practical complexity is O(n · d), but since d is small, it behaves close to O(n) in real scenarios.

What is the best approach for Smallest Index With Digit Sum Equal to Index?

The most practical approach is enumeration with digit sum. Iterate through the array, compute the digit sum of nums[i], and check if it equals the index i. The first match is returned immediately. This solution runs in O(n · d) time where d is the number of digits in each number and uses O(1) extra space.

Is Smallest Index With Digit Sum Equal to Index asked at Google/Amazon/Meta?

This problem represents a typical easy-level screening question focused on array traversal and basic math operations. Variants of digit-sum or index-matching problems appear in coding assessments used by large companies because they test attention to detail and implementation accuracy.

What data structure is used in Smallest Index With Digit Sum Equal to Index?

The primary data structure is a simple array. The algorithm iterates through the array sequentially and performs digit-sum calculations using basic integer arithmetic, without requiring additional data structures like hash maps or stacks.

What is the time complexity of Smallest Index With Digit Sum Equal to Index?

The typical solution runs in O(n · d) time, where n is the array length and d is the number of digits in nums[i]. Each element requires computing its digit sum using repeated division and modulo operations. Space complexity remains O(1) since only a few integer variables are used.

Description Hints 1 Solution Video 3:11

3550. Smallest Index With Digit Sum Equal to Index

Easy84.6% acceptance1 company

You are given an integer array nums.

Return the smallest index i such that the sum of the digits of nums[i] is equal to i.

If no such index exists, return -1.

Example 1:

Input: nums = [1,3,2]

Output: 2

Explanation:

For nums[2] = 2, the sum of digits is 2, which is equal to index i = 2. Thus, the output is 2.

Example 2:

Input: nums = [1,10,11]

Output: 1

Explanation:

For nums[1] = 10, the sum of digits is 1 + 0 = 1, which is equal to index i = 1.
For nums[2] = 11, the sum of digits is 1 + 1 = 2, which is equal to index i = 2.
Since index 1 is the smallest, the output is 1.

Example 3:

Input: nums = [1,2,3]

Output: -1

Explanation:

Since no index satisfies the condition, the output is -1.

Constraints:

1 <= nums.length <= 100
0 <= nums[i] <= 1000

Asked at 1 company

Google

Topics

Array Math

Hints open one at a time

Hint 1

Simulate as described

3:11

Still stuck?Read the written solution, or watch a walkthrough.

Open solution

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1class Solution:
2    def smallestIndex(self, nums: List[int]) -> int:
3        

Starter codePython 3Spaces: 4

Examples

Case 1Case 2Case 3

Input

[1,3,2]

Input

[1,10,11]

Input

[1,2,3]

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