Combination Sum IV

MediumDynamic Programming1d dp

Solve this the way you would in the interview: out loud, on a timer, with an AI interviewer asking follow-ups while you code. You get a scored report at the end.

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Problem

Given an array of **distinct** positive integers nums and a positive integer target, count the ordered sequences of elements from nums that add up to target. Each element may be used any number of times, and sequences that contain the same numbers in a different order are counted separately. The inputs are chosen so the answer fits in a 32-bit signed integer.

Examples

Input: nums = [1,2,3], target = 4
Output: 7
The sequences are (1,1,1,1), (1,1,2), (1,2,1), (2,1,1), (2,2), (1,3), (3,1).
Input: nums = [9], target = 3
Output: 0
No sequence can reach 3.

Constraints

  • 1 <= nums.length <= 200
  • 1 <= nums[i] <= 1000
  • All values in `nums` are distinct
  • 1 <= target <= 1000
  • The answer fits in a 32-bit signed integer

What the interviewer grades

A correct solution is one of five scores. The report also grades problem understanding (did you clarify inputs and edge cases before coding), problem solving, communication while you work, code quality, and testing. See a sample report, or read up on the pattern in the lessons.

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