377. Combination Sum IV

Given an integer array with all positive numbers and no duplicates, find the number of possible combinations that add up to a positive integer target.

Example:

_**nums**_ = [1, 2, 3]
_**target**_ = 4

The possible combination ways are:
(1, 1, 1, 1)
(1, 1, 2)
(1, 2, 1)
(1, 3)
(2, 1, 1)
(2, 2)
(3, 1)

Note that different sequences are counted as different combinations.

Therefore the output is _**7**_.

Follow up: What if negative numbers are allowed in the given array? How does it change the problem? What limitation we need to add to the question to allow negative numbers?

Credits: Special thanks to @pbrother for adding this problem and creating all test cases.

# @lc code=start
using LeetCode

function combination_sum4(nums::Vector{Int}, target::Int)
    dp = OffsetArray(fill(0, target + 1), -1)
    dp[0] = 1
    for i in 1:target, num in nums
        (num <= i) && (dp[i] += dp[i - num])
    end
    return dp[end]
end
# @lc code=end

combination_sum4 (generic function with 1 method)

This page was generated using DemoCards.jl and Literate.jl.