# [377. Combination Sum IV](https://leetcode.com/problems/combination-sum-iv/)

## 题目

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:

```text
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.

## 解题思路

见程序注释
